arc.c revision 288581
1/* 2 * CDDL HEADER START 3 * 4 * The contents of this file are subject to the terms of the 5 * Common Development and Distribution License (the "License"). 6 * You may not use this file except in compliance with the License. 7 * 8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE 9 * or http://www.opensolaris.org/os/licensing. 10 * See the License for the specific language governing permissions 11 * and limitations under the License. 12 * 13 * When distributing Covered Code, include this CDDL HEADER in each 14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE. 15 * If applicable, add the following below this CDDL HEADER, with the 16 * fields enclosed by brackets "[]" replaced with your own identifying 17 * information: Portions Copyright [yyyy] [name of copyright owner] 18 * 19 * CDDL HEADER END 20 */ 21/* 22 * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved. 23 * Copyright (c) 2012, Joyent, Inc. All rights reserved. 24 * Copyright (c) 2011, 2014 by Delphix. All rights reserved. 25 * Copyright (c) 2014 by Saso Kiselkov. All rights reserved. 26 * Copyright 2014 Nexenta Systems, Inc. All rights reserved. 27 */ 28 29/* 30 * DVA-based Adjustable Replacement Cache 31 * 32 * While much of the theory of operation used here is 33 * based on the self-tuning, low overhead replacement cache 34 * presented by Megiddo and Modha at FAST 2003, there are some 35 * significant differences: 36 * 37 * 1. The Megiddo and Modha model assumes any page is evictable. 38 * Pages in its cache cannot be "locked" into memory. This makes 39 * the eviction algorithm simple: evict the last page in the list. 40 * This also make the performance characteristics easy to reason 41 * about. Our cache is not so simple. At any given moment, some 42 * subset of the blocks in the cache are un-evictable because we 43 * have handed out a reference to them. Blocks are only evictable 44 * when there are no external references active. This makes 45 * eviction far more problematic: we choose to evict the evictable 46 * blocks that are the "lowest" in the list. 47 * 48 * There are times when it is not possible to evict the requested 49 * space. In these circumstances we are unable to adjust the cache 50 * size. To prevent the cache growing unbounded at these times we 51 * implement a "cache throttle" that slows the flow of new data 52 * into the cache until we can make space available. 53 * 54 * 2. The Megiddo and Modha model assumes a fixed cache size. 55 * Pages are evicted when the cache is full and there is a cache 56 * miss. Our model has a variable sized cache. It grows with 57 * high use, but also tries to react to memory pressure from the 58 * operating system: decreasing its size when system memory is 59 * tight. 60 * 61 * 3. The Megiddo and Modha model assumes a fixed page size. All 62 * elements of the cache are therefore exactly the same size. So 63 * when adjusting the cache size following a cache miss, its simply 64 * a matter of choosing a single page to evict. In our model, we 65 * have variable sized cache blocks (rangeing from 512 bytes to 66 * 128K bytes). We therefore choose a set of blocks to evict to make 67 * space for a cache miss that approximates as closely as possible 68 * the space used by the new block. 69 * 70 * See also: "ARC: A Self-Tuning, Low Overhead Replacement Cache" 71 * by N. Megiddo & D. Modha, FAST 2003 72 */ 73 74/* 75 * The locking model: 76 * 77 * A new reference to a cache buffer can be obtained in two 78 * ways: 1) via a hash table lookup using the DVA as a key, 79 * or 2) via one of the ARC lists. The arc_read() interface 80 * uses method 1, while the internal arc algorithms for 81 * adjusting the cache use method 2. We therefore provide two 82 * types of locks: 1) the hash table lock array, and 2) the 83 * arc list locks. 84 * 85 * Buffers do not have their own mutexs, rather they rely on the 86 * hash table mutexs for the bulk of their protection (i.e. most 87 * fields in the arc_buf_hdr_t are protected by these mutexs). 88 * 89 * buf_hash_find() returns the appropriate mutex (held) when it 90 * locates the requested buffer in the hash table. It returns 91 * NULL for the mutex if the buffer was not in the table. 92 * 93 * buf_hash_remove() expects the appropriate hash mutex to be 94 * already held before it is invoked. 95 * 96 * Each arc state also has a mutex which is used to protect the 97 * buffer list associated with the state. When attempting to 98 * obtain a hash table lock while holding an arc list lock you 99 * must use: mutex_tryenter() to avoid deadlock. Also note that 100 * the active state mutex must be held before the ghost state mutex. 101 * 102 * Arc buffers may have an associated eviction callback function. 103 * This function will be invoked prior to removing the buffer (e.g. 104 * in arc_do_user_evicts()). Note however that the data associated 105 * with the buffer may be evicted prior to the callback. The callback 106 * must be made with *no locks held* (to prevent deadlock). Additionally, 107 * the users of callbacks must ensure that their private data is 108 * protected from simultaneous callbacks from arc_clear_callback() 109 * and arc_do_user_evicts(). 110 * 111 * Note that the majority of the performance stats are manipulated 112 * with atomic operations. 113 * 114 * The L2ARC uses the l2ad_mtx on each vdev for the following: 115 * 116 * - L2ARC buflist creation 117 * - L2ARC buflist eviction 118 * - L2ARC write completion, which walks L2ARC buflists 119 * - ARC header destruction, as it removes from L2ARC buflists 120 * - ARC header release, as it removes from L2ARC buflists 121 */ 122 123#include <sys/spa.h> 124#include <sys/zio.h> 125#include <sys/zio_compress.h> 126#include <sys/zfs_context.h> 127#include <sys/arc.h> 128#include <sys/refcount.h> 129#include <sys/vdev.h> 130#include <sys/vdev_impl.h> 131#include <sys/dsl_pool.h> 132#include <sys/multilist.h> 133#ifdef _KERNEL 134#include <sys/dnlc.h> 135#endif 136#include <sys/callb.h> 137#include <sys/kstat.h> 138#include <sys/trim_map.h> 139#include <zfs_fletcher.h> 140#include <sys/sdt.h> 141 142#include <vm/vm_pageout.h> 143#include <machine/vmparam.h> 144 145#ifdef illumos 146#ifndef _KERNEL 147/* set with ZFS_DEBUG=watch, to enable watchpoints on frozen buffers */ 148boolean_t arc_watch = B_FALSE; 149int arc_procfd; 150#endif 151#endif /* illumos */ 152 153static kmutex_t arc_reclaim_lock; 154static kcondvar_t arc_reclaim_thread_cv; 155static boolean_t arc_reclaim_thread_exit; 156static kcondvar_t arc_reclaim_waiters_cv; 157 158static kmutex_t arc_user_evicts_lock; 159static kcondvar_t arc_user_evicts_cv; 160static boolean_t arc_user_evicts_thread_exit; 161 162uint_t arc_reduce_dnlc_percent = 3; 163 164/* 165 * The number of headers to evict in arc_evict_state_impl() before 166 * dropping the sublist lock and evicting from another sublist. A lower 167 * value means we're more likely to evict the "correct" header (i.e. the 168 * oldest header in the arc state), but comes with higher overhead 169 * (i.e. more invocations of arc_evict_state_impl()). 170 */ 171int zfs_arc_evict_batch_limit = 10; 172 173/* 174 * The number of sublists used for each of the arc state lists. If this 175 * is not set to a suitable value by the user, it will be configured to 176 * the number of CPUs on the system in arc_init(). 177 */ 178int zfs_arc_num_sublists_per_state = 0; 179 180/* number of seconds before growing cache again */ 181static int arc_grow_retry = 60; 182 183/* shift of arc_c for calculating overflow limit in arc_get_data_buf */ 184int zfs_arc_overflow_shift = 8; 185 186/* shift of arc_c for calculating both min and max arc_p */ 187static int arc_p_min_shift = 4; 188 189/* log2(fraction of arc to reclaim) */ 190static int arc_shrink_shift = 7; 191 192/* 193 * log2(fraction of ARC which must be free to allow growing). 194 * I.e. If there is less than arc_c >> arc_no_grow_shift free memory, 195 * when reading a new block into the ARC, we will evict an equal-sized block 196 * from the ARC. 197 * 198 * This must be less than arc_shrink_shift, so that when we shrink the ARC, 199 * we will still not allow it to grow. 200 */ 201int arc_no_grow_shift = 5; 202 203 204/* 205 * minimum lifespan of a prefetch block in clock ticks 206 * (initialized in arc_init()) 207 */ 208static int arc_min_prefetch_lifespan; 209 210/* 211 * If this percent of memory is free, don't throttle. 212 */ 213int arc_lotsfree_percent = 10; 214 215static int arc_dead; 216extern int zfs_prefetch_disable; 217 218/* 219 * The arc has filled available memory and has now warmed up. 220 */ 221static boolean_t arc_warm; 222 223/* 224 * These tunables are for performance analysis. 225 */ 226uint64_t zfs_arc_max; 227uint64_t zfs_arc_min; 228uint64_t zfs_arc_meta_limit = 0; 229uint64_t zfs_arc_meta_min = 0; 230int zfs_arc_grow_retry = 0; 231int zfs_arc_shrink_shift = 0; 232int zfs_arc_p_min_shift = 0; 233int zfs_disable_dup_eviction = 0; 234uint64_t zfs_arc_average_blocksize = 8 * 1024; /* 8KB */ 235u_int zfs_arc_free_target = 0; 236 237static int sysctl_vfs_zfs_arc_free_target(SYSCTL_HANDLER_ARGS); 238static int sysctl_vfs_zfs_arc_meta_limit(SYSCTL_HANDLER_ARGS); 239 240#ifdef _KERNEL 241static void 242arc_free_target_init(void *unused __unused) 243{ 244 245 zfs_arc_free_target = vm_pageout_wakeup_thresh; 246} 247SYSINIT(arc_free_target_init, SI_SUB_KTHREAD_PAGE, SI_ORDER_ANY, 248 arc_free_target_init, NULL); 249 250TUNABLE_QUAD("vfs.zfs.arc_max", &zfs_arc_max); 251TUNABLE_QUAD("vfs.zfs.arc_min", &zfs_arc_min); 252TUNABLE_QUAD("vfs.zfs.arc_meta_limit", &zfs_arc_meta_limit); 253TUNABLE_QUAD("vfs.zfs.arc_meta_min", &zfs_arc_meta_min); 254TUNABLE_QUAD("vfs.zfs.arc_average_blocksize", &zfs_arc_average_blocksize); 255TUNABLE_INT("vfs.zfs.arc_shrink_shift", &zfs_arc_shrink_shift); 256SYSCTL_DECL(_vfs_zfs); 257SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, arc_max, CTLFLAG_RDTUN, &zfs_arc_max, 0, 258 "Maximum ARC size"); 259SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, arc_min, CTLFLAG_RDTUN, &zfs_arc_min, 0, 260 "Minimum ARC size"); 261SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, arc_average_blocksize, CTLFLAG_RDTUN, 262 &zfs_arc_average_blocksize, 0, 263 "ARC average blocksize"); 264SYSCTL_INT(_vfs_zfs, OID_AUTO, arc_shrink_shift, CTLFLAG_RW, 265 &arc_shrink_shift, 0, 266 "log2(fraction of arc to reclaim)"); 267 268/* 269 * We don't have a tunable for arc_free_target due to the dependency on 270 * pagedaemon initialisation. 271 */ 272SYSCTL_PROC(_vfs_zfs, OID_AUTO, arc_free_target, 273 CTLTYPE_UINT | CTLFLAG_MPSAFE | CTLFLAG_RW, 0, sizeof(u_int), 274 sysctl_vfs_zfs_arc_free_target, "IU", 275 "Desired number of free pages below which ARC triggers reclaim"); 276 277static int 278sysctl_vfs_zfs_arc_free_target(SYSCTL_HANDLER_ARGS) 279{ 280 u_int val; 281 int err; 282 283 val = zfs_arc_free_target; 284 err = sysctl_handle_int(oidp, &val, 0, req); 285 if (err != 0 || req->newptr == NULL) 286 return (err); 287 288 if (val < minfree) 289 return (EINVAL); 290 if (val > cnt.v_page_count) 291 return (EINVAL); 292 293 zfs_arc_free_target = val; 294 295 return (0); 296} 297 298/* 299 * Must be declared here, before the definition of corresponding kstat 300 * macro which uses the same names will confuse the compiler. 301 */ 302SYSCTL_PROC(_vfs_zfs, OID_AUTO, arc_meta_limit, 303 CTLTYPE_U64 | CTLFLAG_MPSAFE | CTLFLAG_RW, 0, sizeof(uint64_t), 304 sysctl_vfs_zfs_arc_meta_limit, "QU", 305 "ARC metadata limit"); 306#endif 307 308/* 309 * Note that buffers can be in one of 6 states: 310 * ARC_anon - anonymous (discussed below) 311 * ARC_mru - recently used, currently cached 312 * ARC_mru_ghost - recentely used, no longer in cache 313 * ARC_mfu - frequently used, currently cached 314 * ARC_mfu_ghost - frequently used, no longer in cache 315 * ARC_l2c_only - exists in L2ARC but not other states 316 * When there are no active references to the buffer, they are 317 * are linked onto a list in one of these arc states. These are 318 * the only buffers that can be evicted or deleted. Within each 319 * state there are multiple lists, one for meta-data and one for 320 * non-meta-data. Meta-data (indirect blocks, blocks of dnodes, 321 * etc.) is tracked separately so that it can be managed more 322 * explicitly: favored over data, limited explicitly. 323 * 324 * Anonymous buffers are buffers that are not associated with 325 * a DVA. These are buffers that hold dirty block copies 326 * before they are written to stable storage. By definition, 327 * they are "ref'd" and are considered part of arc_mru 328 * that cannot be freed. Generally, they will aquire a DVA 329 * as they are written and migrate onto the arc_mru list. 330 * 331 * The ARC_l2c_only state is for buffers that are in the second 332 * level ARC but no longer in any of the ARC_m* lists. The second 333 * level ARC itself may also contain buffers that are in any of 334 * the ARC_m* states - meaning that a buffer can exist in two 335 * places. The reason for the ARC_l2c_only state is to keep the 336 * buffer header in the hash table, so that reads that hit the 337 * second level ARC benefit from these fast lookups. 338 */ 339 340typedef struct arc_state { 341 /* 342 * list of evictable buffers 343 */ 344 multilist_t arcs_list[ARC_BUFC_NUMTYPES]; 345 /* 346 * total amount of evictable data in this state 347 */ 348 uint64_t arcs_lsize[ARC_BUFC_NUMTYPES]; 349 /* 350 * total amount of data in this state; this includes: evictable, 351 * non-evictable, ARC_BUFC_DATA, and ARC_BUFC_METADATA. 352 */ 353 uint64_t arcs_size; 354} arc_state_t; 355 356/* The 6 states: */ 357static arc_state_t ARC_anon; 358static arc_state_t ARC_mru; 359static arc_state_t ARC_mru_ghost; 360static arc_state_t ARC_mfu; 361static arc_state_t ARC_mfu_ghost; 362static arc_state_t ARC_l2c_only; 363 364typedef struct arc_stats { 365 kstat_named_t arcstat_hits; 366 kstat_named_t arcstat_misses; 367 kstat_named_t arcstat_demand_data_hits; 368 kstat_named_t arcstat_demand_data_misses; 369 kstat_named_t arcstat_demand_metadata_hits; 370 kstat_named_t arcstat_demand_metadata_misses; 371 kstat_named_t arcstat_prefetch_data_hits; 372 kstat_named_t arcstat_prefetch_data_misses; 373 kstat_named_t arcstat_prefetch_metadata_hits; 374 kstat_named_t arcstat_prefetch_metadata_misses; 375 kstat_named_t arcstat_mru_hits; 376 kstat_named_t arcstat_mru_ghost_hits; 377 kstat_named_t arcstat_mfu_hits; 378 kstat_named_t arcstat_mfu_ghost_hits; 379 kstat_named_t arcstat_allocated; 380 kstat_named_t arcstat_deleted; 381 /* 382 * Number of buffers that could not be evicted because the hash lock 383 * was held by another thread. The lock may not necessarily be held 384 * by something using the same buffer, since hash locks are shared 385 * by multiple buffers. 386 */ 387 kstat_named_t arcstat_mutex_miss; 388 /* 389 * Number of buffers skipped because they have I/O in progress, are 390 * indrect prefetch buffers that have not lived long enough, or are 391 * not from the spa we're trying to evict from. 392 */ 393 kstat_named_t arcstat_evict_skip; 394 /* 395 * Number of times arc_evict_state() was unable to evict enough 396 * buffers to reach it's target amount. 397 */ 398 kstat_named_t arcstat_evict_not_enough; 399 kstat_named_t arcstat_evict_l2_cached; 400 kstat_named_t arcstat_evict_l2_eligible; 401 kstat_named_t arcstat_evict_l2_ineligible; 402 kstat_named_t arcstat_evict_l2_skip; 403 kstat_named_t arcstat_hash_elements; 404 kstat_named_t arcstat_hash_elements_max; 405 kstat_named_t arcstat_hash_collisions; 406 kstat_named_t arcstat_hash_chains; 407 kstat_named_t arcstat_hash_chain_max; 408 kstat_named_t arcstat_p; 409 kstat_named_t arcstat_c; 410 kstat_named_t arcstat_c_min; 411 kstat_named_t arcstat_c_max; 412 kstat_named_t arcstat_size; 413 /* 414 * Number of bytes consumed by internal ARC structures necessary 415 * for tracking purposes; these structures are not actually 416 * backed by ARC buffers. This includes arc_buf_hdr_t structures 417 * (allocated via arc_buf_hdr_t_full and arc_buf_hdr_t_l2only 418 * caches), and arc_buf_t structures (allocated via arc_buf_t 419 * cache). 420 */ 421 kstat_named_t arcstat_hdr_size; 422 /* 423 * Number of bytes consumed by ARC buffers of type equal to 424 * ARC_BUFC_DATA. This is generally consumed by buffers backing 425 * on disk user data (e.g. plain file contents). 426 */ 427 kstat_named_t arcstat_data_size; 428 /* 429 * Number of bytes consumed by ARC buffers of type equal to 430 * ARC_BUFC_METADATA. This is generally consumed by buffers 431 * backing on disk data that is used for internal ZFS 432 * structures (e.g. ZAP, dnode, indirect blocks, etc). 433 */ 434 kstat_named_t arcstat_metadata_size; 435 /* 436 * Number of bytes consumed by various buffers and structures 437 * not actually backed with ARC buffers. This includes bonus 438 * buffers (allocated directly via zio_buf_* functions), 439 * dmu_buf_impl_t structures (allocated via dmu_buf_impl_t 440 * cache), and dnode_t structures (allocated via dnode_t cache). 441 */ 442 kstat_named_t arcstat_other_size; 443 /* 444 * Total number of bytes consumed by ARC buffers residing in the 445 * arc_anon state. This includes *all* buffers in the arc_anon 446 * state; e.g. data, metadata, evictable, and unevictable buffers 447 * are all included in this value. 448 */ 449 kstat_named_t arcstat_anon_size; 450 /* 451 * Number of bytes consumed by ARC buffers that meet the 452 * following criteria: backing buffers of type ARC_BUFC_DATA, 453 * residing in the arc_anon state, and are eligible for eviction 454 * (e.g. have no outstanding holds on the buffer). 455 */ 456 kstat_named_t arcstat_anon_evictable_data; 457 /* 458 * Number of bytes consumed by ARC buffers that meet the 459 * following criteria: backing buffers of type ARC_BUFC_METADATA, 460 * residing in the arc_anon state, and are eligible for eviction 461 * (e.g. have no outstanding holds on the buffer). 462 */ 463 kstat_named_t arcstat_anon_evictable_metadata; 464 /* 465 * Total number of bytes consumed by ARC buffers residing in the 466 * arc_mru state. This includes *all* buffers in the arc_mru 467 * state; e.g. data, metadata, evictable, and unevictable buffers 468 * are all included in this value. 469 */ 470 kstat_named_t arcstat_mru_size; 471 /* 472 * Number of bytes consumed by ARC buffers that meet the 473 * following criteria: backing buffers of type ARC_BUFC_DATA, 474 * residing in the arc_mru state, and are eligible for eviction 475 * (e.g. have no outstanding holds on the buffer). 476 */ 477 kstat_named_t arcstat_mru_evictable_data; 478 /* 479 * Number of bytes consumed by ARC buffers that meet the 480 * following criteria: backing buffers of type ARC_BUFC_METADATA, 481 * residing in the arc_mru state, and are eligible for eviction 482 * (e.g. have no outstanding holds on the buffer). 483 */ 484 kstat_named_t arcstat_mru_evictable_metadata; 485 /* 486 * Total number of bytes that *would have been* consumed by ARC 487 * buffers in the arc_mru_ghost state. The key thing to note 488 * here, is the fact that this size doesn't actually indicate 489 * RAM consumption. The ghost lists only consist of headers and 490 * don't actually have ARC buffers linked off of these headers. 491 * Thus, *if* the headers had associated ARC buffers, these 492 * buffers *would have* consumed this number of bytes. 493 */ 494 kstat_named_t arcstat_mru_ghost_size; 495 /* 496 * Number of bytes that *would have been* consumed by ARC 497 * buffers that are eligible for eviction, of type 498 * ARC_BUFC_DATA, and linked off the arc_mru_ghost state. 499 */ 500 kstat_named_t arcstat_mru_ghost_evictable_data; 501 /* 502 * Number of bytes that *would have been* consumed by ARC 503 * buffers that are eligible for eviction, of type 504 * ARC_BUFC_METADATA, and linked off the arc_mru_ghost state. 505 */ 506 kstat_named_t arcstat_mru_ghost_evictable_metadata; 507 /* 508 * Total number of bytes consumed by ARC buffers residing in the 509 * arc_mfu state. This includes *all* buffers in the arc_mfu 510 * state; e.g. data, metadata, evictable, and unevictable buffers 511 * are all included in this value. 512 */ 513 kstat_named_t arcstat_mfu_size; 514 /* 515 * Number of bytes consumed by ARC buffers that are eligible for 516 * eviction, of type ARC_BUFC_DATA, and reside in the arc_mfu 517 * state. 518 */ 519 kstat_named_t arcstat_mfu_evictable_data; 520 /* 521 * Number of bytes consumed by ARC buffers that are eligible for 522 * eviction, of type ARC_BUFC_METADATA, and reside in the 523 * arc_mfu state. 524 */ 525 kstat_named_t arcstat_mfu_evictable_metadata; 526 /* 527 * Total number of bytes that *would have been* consumed by ARC 528 * buffers in the arc_mfu_ghost state. See the comment above 529 * arcstat_mru_ghost_size for more details. 530 */ 531 kstat_named_t arcstat_mfu_ghost_size; 532 /* 533 * Number of bytes that *would have been* consumed by ARC 534 * buffers that are eligible for eviction, of type 535 * ARC_BUFC_DATA, and linked off the arc_mfu_ghost state. 536 */ 537 kstat_named_t arcstat_mfu_ghost_evictable_data; 538 /* 539 * Number of bytes that *would have been* consumed by ARC 540 * buffers that are eligible for eviction, of type 541 * ARC_BUFC_METADATA, and linked off the arc_mru_ghost state. 542 */ 543 kstat_named_t arcstat_mfu_ghost_evictable_metadata; 544 kstat_named_t arcstat_l2_hits; 545 kstat_named_t arcstat_l2_misses; 546 kstat_named_t arcstat_l2_feeds; 547 kstat_named_t arcstat_l2_rw_clash; 548 kstat_named_t arcstat_l2_read_bytes; 549 kstat_named_t arcstat_l2_write_bytes; 550 kstat_named_t arcstat_l2_writes_sent; 551 kstat_named_t arcstat_l2_writes_done; 552 kstat_named_t arcstat_l2_writes_error; 553 kstat_named_t arcstat_l2_writes_lock_retry; 554 kstat_named_t arcstat_l2_evict_lock_retry; 555 kstat_named_t arcstat_l2_evict_reading; 556 kstat_named_t arcstat_l2_evict_l1cached; 557 kstat_named_t arcstat_l2_free_on_write; 558 kstat_named_t arcstat_l2_cdata_free_on_write; 559 kstat_named_t arcstat_l2_abort_lowmem; 560 kstat_named_t arcstat_l2_cksum_bad; 561 kstat_named_t arcstat_l2_io_error; 562 kstat_named_t arcstat_l2_size; 563 kstat_named_t arcstat_l2_asize; 564 kstat_named_t arcstat_l2_hdr_size; 565 kstat_named_t arcstat_l2_compress_successes; 566 kstat_named_t arcstat_l2_compress_zeros; 567 kstat_named_t arcstat_l2_compress_failures; 568 kstat_named_t arcstat_l2_write_trylock_fail; 569 kstat_named_t arcstat_l2_write_passed_headroom; 570 kstat_named_t arcstat_l2_write_spa_mismatch; 571 kstat_named_t arcstat_l2_write_in_l2; 572 kstat_named_t arcstat_l2_write_hdr_io_in_progress; 573 kstat_named_t arcstat_l2_write_not_cacheable; 574 kstat_named_t arcstat_l2_write_full; 575 kstat_named_t arcstat_l2_write_buffer_iter; 576 kstat_named_t arcstat_l2_write_pios; 577 kstat_named_t arcstat_l2_write_buffer_bytes_scanned; 578 kstat_named_t arcstat_l2_write_buffer_list_iter; 579 kstat_named_t arcstat_l2_write_buffer_list_null_iter; 580 kstat_named_t arcstat_memory_throttle_count; 581 kstat_named_t arcstat_duplicate_buffers; 582 kstat_named_t arcstat_duplicate_buffers_size; 583 kstat_named_t arcstat_duplicate_reads; 584 kstat_named_t arcstat_meta_used; 585 kstat_named_t arcstat_meta_limit; 586 kstat_named_t arcstat_meta_max; 587 kstat_named_t arcstat_meta_min; 588} arc_stats_t; 589 590static arc_stats_t arc_stats = { 591 { "hits", KSTAT_DATA_UINT64 }, 592 { "misses", KSTAT_DATA_UINT64 }, 593 { "demand_data_hits", KSTAT_DATA_UINT64 }, 594 { "demand_data_misses", KSTAT_DATA_UINT64 }, 595 { "demand_metadata_hits", KSTAT_DATA_UINT64 }, 596 { "demand_metadata_misses", KSTAT_DATA_UINT64 }, 597 { "prefetch_data_hits", KSTAT_DATA_UINT64 }, 598 { "prefetch_data_misses", KSTAT_DATA_UINT64 }, 599 { "prefetch_metadata_hits", KSTAT_DATA_UINT64 }, 600 { "prefetch_metadata_misses", KSTAT_DATA_UINT64 }, 601 { "mru_hits", KSTAT_DATA_UINT64 }, 602 { "mru_ghost_hits", KSTAT_DATA_UINT64 }, 603 { "mfu_hits", KSTAT_DATA_UINT64 }, 604 { "mfu_ghost_hits", KSTAT_DATA_UINT64 }, 605 { "allocated", KSTAT_DATA_UINT64 }, 606 { "deleted", KSTAT_DATA_UINT64 }, 607 { "mutex_miss", KSTAT_DATA_UINT64 }, 608 { "evict_skip", KSTAT_DATA_UINT64 }, 609 { "evict_not_enough", KSTAT_DATA_UINT64 }, 610 { "evict_l2_cached", KSTAT_DATA_UINT64 }, 611 { "evict_l2_eligible", KSTAT_DATA_UINT64 }, 612 { "evict_l2_ineligible", KSTAT_DATA_UINT64 }, 613 { "evict_l2_skip", KSTAT_DATA_UINT64 }, 614 { "hash_elements", KSTAT_DATA_UINT64 }, 615 { "hash_elements_max", KSTAT_DATA_UINT64 }, 616 { "hash_collisions", KSTAT_DATA_UINT64 }, 617 { "hash_chains", KSTAT_DATA_UINT64 }, 618 { "hash_chain_max", KSTAT_DATA_UINT64 }, 619 { "p", KSTAT_DATA_UINT64 }, 620 { "c", KSTAT_DATA_UINT64 }, 621 { "c_min", KSTAT_DATA_UINT64 }, 622 { "c_max", KSTAT_DATA_UINT64 }, 623 { "size", KSTAT_DATA_UINT64 }, 624 { "hdr_size", KSTAT_DATA_UINT64 }, 625 { "data_size", KSTAT_DATA_UINT64 }, 626 { "metadata_size", KSTAT_DATA_UINT64 }, 627 { "other_size", KSTAT_DATA_UINT64 }, 628 { "anon_size", KSTAT_DATA_UINT64 }, 629 { "anon_evictable_data", KSTAT_DATA_UINT64 }, 630 { "anon_evictable_metadata", KSTAT_DATA_UINT64 }, 631 { "mru_size", KSTAT_DATA_UINT64 }, 632 { "mru_evictable_data", KSTAT_DATA_UINT64 }, 633 { "mru_evictable_metadata", KSTAT_DATA_UINT64 }, 634 { "mru_ghost_size", KSTAT_DATA_UINT64 }, 635 { "mru_ghost_evictable_data", KSTAT_DATA_UINT64 }, 636 { "mru_ghost_evictable_metadata", KSTAT_DATA_UINT64 }, 637 { "mfu_size", KSTAT_DATA_UINT64 }, 638 { "mfu_evictable_data", KSTAT_DATA_UINT64 }, 639 { "mfu_evictable_metadata", KSTAT_DATA_UINT64 }, 640 { "mfu_ghost_size", KSTAT_DATA_UINT64 }, 641 { "mfu_ghost_evictable_data", KSTAT_DATA_UINT64 }, 642 { "mfu_ghost_evictable_metadata", KSTAT_DATA_UINT64 }, 643 { "l2_hits", KSTAT_DATA_UINT64 }, 644 { "l2_misses", KSTAT_DATA_UINT64 }, 645 { "l2_feeds", KSTAT_DATA_UINT64 }, 646 { "l2_rw_clash", KSTAT_DATA_UINT64 }, 647 { "l2_read_bytes", KSTAT_DATA_UINT64 }, 648 { "l2_write_bytes", KSTAT_DATA_UINT64 }, 649 { "l2_writes_sent", KSTAT_DATA_UINT64 }, 650 { "l2_writes_done", KSTAT_DATA_UINT64 }, 651 { "l2_writes_error", KSTAT_DATA_UINT64 }, 652 { "l2_writes_lock_retry", KSTAT_DATA_UINT64 }, 653 { "l2_evict_lock_retry", KSTAT_DATA_UINT64 }, 654 { "l2_evict_reading", KSTAT_DATA_UINT64 }, 655 { "l2_evict_l1cached", KSTAT_DATA_UINT64 }, 656 { "l2_free_on_write", KSTAT_DATA_UINT64 }, 657 { "l2_cdata_free_on_write", KSTAT_DATA_UINT64 }, 658 { "l2_abort_lowmem", KSTAT_DATA_UINT64 }, 659 { "l2_cksum_bad", KSTAT_DATA_UINT64 }, 660 { "l2_io_error", KSTAT_DATA_UINT64 }, 661 { "l2_size", KSTAT_DATA_UINT64 }, 662 { "l2_asize", KSTAT_DATA_UINT64 }, 663 { "l2_hdr_size", KSTAT_DATA_UINT64 }, 664 { "l2_compress_successes", KSTAT_DATA_UINT64 }, 665 { "l2_compress_zeros", KSTAT_DATA_UINT64 }, 666 { "l2_compress_failures", KSTAT_DATA_UINT64 }, 667 { "l2_write_trylock_fail", KSTAT_DATA_UINT64 }, 668 { "l2_write_passed_headroom", KSTAT_DATA_UINT64 }, 669 { "l2_write_spa_mismatch", KSTAT_DATA_UINT64 }, 670 { "l2_write_in_l2", KSTAT_DATA_UINT64 }, 671 { "l2_write_io_in_progress", KSTAT_DATA_UINT64 }, 672 { "l2_write_not_cacheable", KSTAT_DATA_UINT64 }, 673 { "l2_write_full", KSTAT_DATA_UINT64 }, 674 { "l2_write_buffer_iter", KSTAT_DATA_UINT64 }, 675 { "l2_write_pios", KSTAT_DATA_UINT64 }, 676 { "l2_write_buffer_bytes_scanned", KSTAT_DATA_UINT64 }, 677 { "l2_write_buffer_list_iter", KSTAT_DATA_UINT64 }, 678 { "l2_write_buffer_list_null_iter", KSTAT_DATA_UINT64 }, 679 { "memory_throttle_count", KSTAT_DATA_UINT64 }, 680 { "duplicate_buffers", KSTAT_DATA_UINT64 }, 681 { "duplicate_buffers_size", KSTAT_DATA_UINT64 }, 682 { "duplicate_reads", KSTAT_DATA_UINT64 }, 683 { "arc_meta_used", KSTAT_DATA_UINT64 }, 684 { "arc_meta_limit", KSTAT_DATA_UINT64 }, 685 { "arc_meta_max", KSTAT_DATA_UINT64 }, 686 { "arc_meta_min", KSTAT_DATA_UINT64 } 687}; 688 689#define ARCSTAT(stat) (arc_stats.stat.value.ui64) 690 691#define ARCSTAT_INCR(stat, val) \ 692 atomic_add_64(&arc_stats.stat.value.ui64, (val)) 693 694#define ARCSTAT_BUMP(stat) ARCSTAT_INCR(stat, 1) 695#define ARCSTAT_BUMPDOWN(stat) ARCSTAT_INCR(stat, -1) 696 697#define ARCSTAT_MAX(stat, val) { \ 698 uint64_t m; \ 699 while ((val) > (m = arc_stats.stat.value.ui64) && \ 700 (m != atomic_cas_64(&arc_stats.stat.value.ui64, m, (val)))) \ 701 continue; \ 702} 703 704#define ARCSTAT_MAXSTAT(stat) \ 705 ARCSTAT_MAX(stat##_max, arc_stats.stat.value.ui64) 706 707/* 708 * We define a macro to allow ARC hits/misses to be easily broken down by 709 * two separate conditions, giving a total of four different subtypes for 710 * each of hits and misses (so eight statistics total). 711 */ 712#define ARCSTAT_CONDSTAT(cond1, stat1, notstat1, cond2, stat2, notstat2, stat) \ 713 if (cond1) { \ 714 if (cond2) { \ 715 ARCSTAT_BUMP(arcstat_##stat1##_##stat2##_##stat); \ 716 } else { \ 717 ARCSTAT_BUMP(arcstat_##stat1##_##notstat2##_##stat); \ 718 } \ 719 } else { \ 720 if (cond2) { \ 721 ARCSTAT_BUMP(arcstat_##notstat1##_##stat2##_##stat); \ 722 } else { \ 723 ARCSTAT_BUMP(arcstat_##notstat1##_##notstat2##_##stat);\ 724 } \ 725 } 726 727kstat_t *arc_ksp; 728static arc_state_t *arc_anon; 729static arc_state_t *arc_mru; 730static arc_state_t *arc_mru_ghost; 731static arc_state_t *arc_mfu; 732static arc_state_t *arc_mfu_ghost; 733static arc_state_t *arc_l2c_only; 734 735/* 736 * There are several ARC variables that are critical to export as kstats -- 737 * but we don't want to have to grovel around in the kstat whenever we wish to 738 * manipulate them. For these variables, we therefore define them to be in 739 * terms of the statistic variable. This assures that we are not introducing 740 * the possibility of inconsistency by having shadow copies of the variables, 741 * while still allowing the code to be readable. 742 */ 743#define arc_size ARCSTAT(arcstat_size) /* actual total arc size */ 744#define arc_p ARCSTAT(arcstat_p) /* target size of MRU */ 745#define arc_c ARCSTAT(arcstat_c) /* target size of cache */ 746#define arc_c_min ARCSTAT(arcstat_c_min) /* min target cache size */ 747#define arc_c_max ARCSTAT(arcstat_c_max) /* max target cache size */ 748#define arc_meta_limit ARCSTAT(arcstat_meta_limit) /* max size for metadata */ 749#define arc_meta_min ARCSTAT(arcstat_meta_min) /* min size for metadata */ 750#define arc_meta_used ARCSTAT(arcstat_meta_used) /* size of metadata */ 751#define arc_meta_max ARCSTAT(arcstat_meta_max) /* max size of metadata */ 752 753#define L2ARC_IS_VALID_COMPRESS(_c_) \ 754 ((_c_) == ZIO_COMPRESS_LZ4 || (_c_) == ZIO_COMPRESS_EMPTY) 755 756static int arc_no_grow; /* Don't try to grow cache size */ 757static uint64_t arc_tempreserve; 758static uint64_t arc_loaned_bytes; 759 760typedef struct arc_callback arc_callback_t; 761 762struct arc_callback { 763 void *acb_private; 764 arc_done_func_t *acb_done; 765 arc_buf_t *acb_buf; 766 zio_t *acb_zio_dummy; 767 arc_callback_t *acb_next; 768}; 769 770typedef struct arc_write_callback arc_write_callback_t; 771 772struct arc_write_callback { 773 void *awcb_private; 774 arc_done_func_t *awcb_ready; 775 arc_done_func_t *awcb_physdone; 776 arc_done_func_t *awcb_done; 777 arc_buf_t *awcb_buf; 778}; 779 780/* 781 * ARC buffers are separated into multiple structs as a memory saving measure: 782 * - Common fields struct, always defined, and embedded within it: 783 * - L2-only fields, always allocated but undefined when not in L2ARC 784 * - L1-only fields, only allocated when in L1ARC 785 * 786 * Buffer in L1 Buffer only in L2 787 * +------------------------+ +------------------------+ 788 * | arc_buf_hdr_t | | arc_buf_hdr_t | 789 * | | | | 790 * | | | | 791 * | | | | 792 * +------------------------+ +------------------------+ 793 * | l2arc_buf_hdr_t | | l2arc_buf_hdr_t | 794 * | (undefined if L1-only) | | | 795 * +------------------------+ +------------------------+ 796 * | l1arc_buf_hdr_t | 797 * | | 798 * | | 799 * | | 800 * | | 801 * +------------------------+ 802 * 803 * Because it's possible for the L2ARC to become extremely large, we can wind 804 * up eating a lot of memory in L2ARC buffer headers, so the size of a header 805 * is minimized by only allocating the fields necessary for an L1-cached buffer 806 * when a header is actually in the L1 cache. The sub-headers (l1arc_buf_hdr and 807 * l2arc_buf_hdr) are embedded rather than allocated separately to save a couple 808 * words in pointers. arc_hdr_realloc() is used to switch a header between 809 * these two allocation states. 810 */ 811typedef struct l1arc_buf_hdr { 812 kmutex_t b_freeze_lock; 813#ifdef ZFS_DEBUG 814 /* 815 * used for debugging wtih kmem_flags - by allocating and freeing 816 * b_thawed when the buffer is thawed, we get a record of the stack 817 * trace that thawed it. 818 */ 819 void *b_thawed; 820#endif 821 822 arc_buf_t *b_buf; 823 uint32_t b_datacnt; 824 /* for waiting on writes to complete */ 825 kcondvar_t b_cv; 826 827 /* protected by arc state mutex */ 828 arc_state_t *b_state; 829 multilist_node_t b_arc_node; 830 831 /* updated atomically */ 832 clock_t b_arc_access; 833 834 /* self protecting */ 835 refcount_t b_refcnt; 836 837 arc_callback_t *b_acb; 838 /* temporary buffer holder for in-flight compressed data */ 839 void *b_tmp_cdata; 840} l1arc_buf_hdr_t; 841 842typedef struct l2arc_dev l2arc_dev_t; 843 844typedef struct l2arc_buf_hdr { 845 /* protected by arc_buf_hdr mutex */ 846 l2arc_dev_t *b_dev; /* L2ARC device */ 847 uint64_t b_daddr; /* disk address, offset byte */ 848 /* real alloc'd buffer size depending on b_compress applied */ 849 int32_t b_asize; 850 851 list_node_t b_l2node; 852} l2arc_buf_hdr_t; 853 854struct arc_buf_hdr { 855 /* protected by hash lock */ 856 dva_t b_dva; 857 uint64_t b_birth; 858 /* 859 * Even though this checksum is only set/verified when a buffer is in 860 * the L1 cache, it needs to be in the set of common fields because it 861 * must be preserved from the time before a buffer is written out to 862 * L2ARC until after it is read back in. 863 */ 864 zio_cksum_t *b_freeze_cksum; 865 866 arc_buf_hdr_t *b_hash_next; 867 arc_flags_t b_flags; 868 869 /* immutable */ 870 int32_t b_size; 871 uint64_t b_spa; 872 873 /* L2ARC fields. Undefined when not in L2ARC. */ 874 l2arc_buf_hdr_t b_l2hdr; 875 /* L1ARC fields. Undefined when in l2arc_only state */ 876 l1arc_buf_hdr_t b_l1hdr; 877}; 878 879#ifdef _KERNEL 880static int 881sysctl_vfs_zfs_arc_meta_limit(SYSCTL_HANDLER_ARGS) 882{ 883 uint64_t val; 884 int err; 885 886 val = arc_meta_limit; 887 err = sysctl_handle_64(oidp, &val, 0, req); 888 if (err != 0 || req->newptr == NULL) 889 return (err); 890 891 if (val <= 0 || val > arc_c_max) 892 return (EINVAL); 893 894 arc_meta_limit = val; 895 return (0); 896} 897#endif 898 899static arc_buf_t *arc_eviction_list; 900static arc_buf_hdr_t arc_eviction_hdr; 901 902#define GHOST_STATE(state) \ 903 ((state) == arc_mru_ghost || (state) == arc_mfu_ghost || \ 904 (state) == arc_l2c_only) 905 906#define HDR_IN_HASH_TABLE(hdr) ((hdr)->b_flags & ARC_FLAG_IN_HASH_TABLE) 907#define HDR_IO_IN_PROGRESS(hdr) ((hdr)->b_flags & ARC_FLAG_IO_IN_PROGRESS) 908#define HDR_IO_ERROR(hdr) ((hdr)->b_flags & ARC_FLAG_IO_ERROR) 909#define HDR_PREFETCH(hdr) ((hdr)->b_flags & ARC_FLAG_PREFETCH) 910#define HDR_FREED_IN_READ(hdr) ((hdr)->b_flags & ARC_FLAG_FREED_IN_READ) 911#define HDR_BUF_AVAILABLE(hdr) ((hdr)->b_flags & ARC_FLAG_BUF_AVAILABLE) 912 913#define HDR_L2CACHE(hdr) ((hdr)->b_flags & ARC_FLAG_L2CACHE) 914#define HDR_L2COMPRESS(hdr) ((hdr)->b_flags & ARC_FLAG_L2COMPRESS) 915#define HDR_L2_READING(hdr) \ 916 (((hdr)->b_flags & ARC_FLAG_IO_IN_PROGRESS) && \ 917 ((hdr)->b_flags & ARC_FLAG_HAS_L2HDR)) 918#define HDR_L2_WRITING(hdr) ((hdr)->b_flags & ARC_FLAG_L2_WRITING) 919#define HDR_L2_EVICTED(hdr) ((hdr)->b_flags & ARC_FLAG_L2_EVICTED) 920#define HDR_L2_WRITE_HEAD(hdr) ((hdr)->b_flags & ARC_FLAG_L2_WRITE_HEAD) 921 922#define HDR_ISTYPE_METADATA(hdr) \ 923 ((hdr)->b_flags & ARC_FLAG_BUFC_METADATA) 924#define HDR_ISTYPE_DATA(hdr) (!HDR_ISTYPE_METADATA(hdr)) 925 926#define HDR_HAS_L1HDR(hdr) ((hdr)->b_flags & ARC_FLAG_HAS_L1HDR) 927#define HDR_HAS_L2HDR(hdr) ((hdr)->b_flags & ARC_FLAG_HAS_L2HDR) 928 929/* For storing compression mode in b_flags */ 930#define HDR_COMPRESS_OFFSET 24 931#define HDR_COMPRESS_NBITS 7 932 933#define HDR_GET_COMPRESS(hdr) ((enum zio_compress)BF32_GET(hdr->b_flags, \ 934 HDR_COMPRESS_OFFSET, HDR_COMPRESS_NBITS)) 935#define HDR_SET_COMPRESS(hdr, cmp) BF32_SET(hdr->b_flags, \ 936 HDR_COMPRESS_OFFSET, HDR_COMPRESS_NBITS, (cmp)) 937 938/* 939 * Other sizes 940 */ 941 942#define HDR_FULL_SIZE ((int64_t)sizeof (arc_buf_hdr_t)) 943#define HDR_L2ONLY_SIZE ((int64_t)offsetof(arc_buf_hdr_t, b_l1hdr)) 944 945/* 946 * Hash table routines 947 */ 948 949#define HT_LOCK_PAD CACHE_LINE_SIZE 950 951struct ht_lock { 952 kmutex_t ht_lock; 953#ifdef _KERNEL 954 unsigned char pad[(HT_LOCK_PAD - sizeof (kmutex_t))]; 955#endif 956}; 957 958#define BUF_LOCKS 256 959typedef struct buf_hash_table { 960 uint64_t ht_mask; 961 arc_buf_hdr_t **ht_table; 962 struct ht_lock ht_locks[BUF_LOCKS] __aligned(CACHE_LINE_SIZE); 963} buf_hash_table_t; 964 965static buf_hash_table_t buf_hash_table; 966 967#define BUF_HASH_INDEX(spa, dva, birth) \ 968 (buf_hash(spa, dva, birth) & buf_hash_table.ht_mask) 969#define BUF_HASH_LOCK_NTRY(idx) (buf_hash_table.ht_locks[idx & (BUF_LOCKS-1)]) 970#define BUF_HASH_LOCK(idx) (&(BUF_HASH_LOCK_NTRY(idx).ht_lock)) 971#define HDR_LOCK(hdr) \ 972 (BUF_HASH_LOCK(BUF_HASH_INDEX(hdr->b_spa, &hdr->b_dva, hdr->b_birth))) 973 974uint64_t zfs_crc64_table[256]; 975 976/* 977 * Level 2 ARC 978 */ 979 980#define L2ARC_WRITE_SIZE (8 * 1024 * 1024) /* initial write max */ 981#define L2ARC_HEADROOM 2 /* num of writes */ 982/* 983 * If we discover during ARC scan any buffers to be compressed, we boost 984 * our headroom for the next scanning cycle by this percentage multiple. 985 */ 986#define L2ARC_HEADROOM_BOOST 200 987#define L2ARC_FEED_SECS 1 /* caching interval secs */ 988#define L2ARC_FEED_MIN_MS 200 /* min caching interval ms */ 989 990/* 991 * Used to distinguish headers that are being process by 992 * l2arc_write_buffers(), but have yet to be assigned to a l2arc disk 993 * address. This can happen when the header is added to the l2arc's list 994 * of buffers to write in the first stage of l2arc_write_buffers(), but 995 * has not yet been written out which happens in the second stage of 996 * l2arc_write_buffers(). 997 */ 998#define L2ARC_ADDR_UNSET ((uint64_t)(-1)) 999 1000#define l2arc_writes_sent ARCSTAT(arcstat_l2_writes_sent) 1001#define l2arc_writes_done ARCSTAT(arcstat_l2_writes_done) 1002 1003/* L2ARC Performance Tunables */ 1004uint64_t l2arc_write_max = L2ARC_WRITE_SIZE; /* default max write size */ 1005uint64_t l2arc_write_boost = L2ARC_WRITE_SIZE; /* extra write during warmup */ 1006uint64_t l2arc_headroom = L2ARC_HEADROOM; /* number of dev writes */ 1007uint64_t l2arc_headroom_boost = L2ARC_HEADROOM_BOOST; 1008uint64_t l2arc_feed_secs = L2ARC_FEED_SECS; /* interval seconds */ 1009uint64_t l2arc_feed_min_ms = L2ARC_FEED_MIN_MS; /* min interval milliseconds */ 1010boolean_t l2arc_noprefetch = B_TRUE; /* don't cache prefetch bufs */ 1011boolean_t l2arc_feed_again = B_TRUE; /* turbo warmup */ 1012boolean_t l2arc_norw = B_TRUE; /* no reads during writes */ 1013 1014SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, l2arc_write_max, CTLFLAG_RW, 1015 &l2arc_write_max, 0, "max write size"); 1016SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, l2arc_write_boost, CTLFLAG_RW, 1017 &l2arc_write_boost, 0, "extra write during warmup"); 1018SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, l2arc_headroom, CTLFLAG_RW, 1019 &l2arc_headroom, 0, "number of dev writes"); 1020SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, l2arc_feed_secs, CTLFLAG_RW, 1021 &l2arc_feed_secs, 0, "interval seconds"); 1022SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, l2arc_feed_min_ms, CTLFLAG_RW, 1023 &l2arc_feed_min_ms, 0, "min interval milliseconds"); 1024 1025SYSCTL_INT(_vfs_zfs, OID_AUTO, l2arc_noprefetch, CTLFLAG_RW, 1026 &l2arc_noprefetch, 0, "don't cache prefetch bufs"); 1027SYSCTL_INT(_vfs_zfs, OID_AUTO, l2arc_feed_again, CTLFLAG_RW, 1028 &l2arc_feed_again, 0, "turbo warmup"); 1029SYSCTL_INT(_vfs_zfs, OID_AUTO, l2arc_norw, CTLFLAG_RW, 1030 &l2arc_norw, 0, "no reads during writes"); 1031 1032SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, anon_size, CTLFLAG_RD, 1033 &ARC_anon.arcs_size, 0, "size of anonymous state"); 1034SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, anon_metadata_lsize, CTLFLAG_RD, 1035 &ARC_anon.arcs_lsize[ARC_BUFC_METADATA], 0, "size of anonymous state"); 1036SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, anon_data_lsize, CTLFLAG_RD, 1037 &ARC_anon.arcs_lsize[ARC_BUFC_DATA], 0, "size of anonymous state"); 1038 1039SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, mru_size, CTLFLAG_RD, 1040 &ARC_mru.arcs_size, 0, "size of mru state"); 1041SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, mru_metadata_lsize, CTLFLAG_RD, 1042 &ARC_mru.arcs_lsize[ARC_BUFC_METADATA], 0, "size of metadata in mru state"); 1043SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, mru_data_lsize, CTLFLAG_RD, 1044 &ARC_mru.arcs_lsize[ARC_BUFC_DATA], 0, "size of data in mru state"); 1045 1046SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, mru_ghost_size, CTLFLAG_RD, 1047 &ARC_mru_ghost.arcs_size, 0, "size of mru ghost state"); 1048SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, mru_ghost_metadata_lsize, CTLFLAG_RD, 1049 &ARC_mru_ghost.arcs_lsize[ARC_BUFC_METADATA], 0, 1050 "size of metadata in mru ghost state"); 1051SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, mru_ghost_data_lsize, CTLFLAG_RD, 1052 &ARC_mru_ghost.arcs_lsize[ARC_BUFC_DATA], 0, 1053 "size of data in mru ghost state"); 1054 1055SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, mfu_size, CTLFLAG_RD, 1056 &ARC_mfu.arcs_size, 0, "size of mfu state"); 1057SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, mfu_metadata_lsize, CTLFLAG_RD, 1058 &ARC_mfu.arcs_lsize[ARC_BUFC_METADATA], 0, "size of metadata in mfu state"); 1059SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, mfu_data_lsize, CTLFLAG_RD, 1060 &ARC_mfu.arcs_lsize[ARC_BUFC_DATA], 0, "size of data in mfu state"); 1061 1062SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, mfu_ghost_size, CTLFLAG_RD, 1063 &ARC_mfu_ghost.arcs_size, 0, "size of mfu ghost state"); 1064SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, mfu_ghost_metadata_lsize, CTLFLAG_RD, 1065 &ARC_mfu_ghost.arcs_lsize[ARC_BUFC_METADATA], 0, 1066 "size of metadata in mfu ghost state"); 1067SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, mfu_ghost_data_lsize, CTLFLAG_RD, 1068 &ARC_mfu_ghost.arcs_lsize[ARC_BUFC_DATA], 0, 1069 "size of data in mfu ghost state"); 1070 1071SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, l2c_only_size, CTLFLAG_RD, 1072 &ARC_l2c_only.arcs_size, 0, "size of mru state"); 1073 1074/* 1075 * L2ARC Internals 1076 */ 1077struct l2arc_dev { 1078 vdev_t *l2ad_vdev; /* vdev */ 1079 spa_t *l2ad_spa; /* spa */ 1080 uint64_t l2ad_hand; /* next write location */ 1081 uint64_t l2ad_start; /* first addr on device */ 1082 uint64_t l2ad_end; /* last addr on device */ 1083 boolean_t l2ad_first; /* first sweep through */ 1084 boolean_t l2ad_writing; /* currently writing */ 1085 kmutex_t l2ad_mtx; /* lock for buffer list */ 1086 list_t l2ad_buflist; /* buffer list */ 1087 list_node_t l2ad_node; /* device list node */ 1088 refcount_t l2ad_alloc; /* allocated bytes */ 1089}; 1090 1091static list_t L2ARC_dev_list; /* device list */ 1092static list_t *l2arc_dev_list; /* device list pointer */ 1093static kmutex_t l2arc_dev_mtx; /* device list mutex */ 1094static l2arc_dev_t *l2arc_dev_last; /* last device used */ 1095static list_t L2ARC_free_on_write; /* free after write buf list */ 1096static list_t *l2arc_free_on_write; /* free after write list ptr */ 1097static kmutex_t l2arc_free_on_write_mtx; /* mutex for list */ 1098static uint64_t l2arc_ndev; /* number of devices */ 1099 1100typedef struct l2arc_read_callback { 1101 arc_buf_t *l2rcb_buf; /* read buffer */ 1102 spa_t *l2rcb_spa; /* spa */ 1103 blkptr_t l2rcb_bp; /* original blkptr */ 1104 zbookmark_phys_t l2rcb_zb; /* original bookmark */ 1105 int l2rcb_flags; /* original flags */ 1106 enum zio_compress l2rcb_compress; /* applied compress */ 1107} l2arc_read_callback_t; 1108 1109typedef struct l2arc_write_callback { 1110 l2arc_dev_t *l2wcb_dev; /* device info */ 1111 arc_buf_hdr_t *l2wcb_head; /* head of write buflist */ 1112} l2arc_write_callback_t; 1113 1114typedef struct l2arc_data_free { 1115 /* protected by l2arc_free_on_write_mtx */ 1116 void *l2df_data; 1117 size_t l2df_size; 1118 void (*l2df_func)(void *, size_t); 1119 list_node_t l2df_list_node; 1120} l2arc_data_free_t; 1121 1122static kmutex_t l2arc_feed_thr_lock; 1123static kcondvar_t l2arc_feed_thr_cv; 1124static uint8_t l2arc_thread_exit; 1125 1126static void arc_get_data_buf(arc_buf_t *); 1127static void arc_access(arc_buf_hdr_t *, kmutex_t *); 1128static boolean_t arc_is_overflowing(); 1129static void arc_buf_watch(arc_buf_t *); 1130 1131static arc_buf_contents_t arc_buf_type(arc_buf_hdr_t *); 1132static uint32_t arc_bufc_to_flags(arc_buf_contents_t); 1133 1134static boolean_t l2arc_write_eligible(uint64_t, arc_buf_hdr_t *); 1135static void l2arc_read_done(zio_t *); 1136 1137static boolean_t l2arc_compress_buf(arc_buf_hdr_t *); 1138static void l2arc_decompress_zio(zio_t *, arc_buf_hdr_t *, enum zio_compress); 1139static void l2arc_release_cdata_buf(arc_buf_hdr_t *); 1140 1141static uint64_t 1142buf_hash(uint64_t spa, const dva_t *dva, uint64_t birth) 1143{ 1144 uint8_t *vdva = (uint8_t *)dva; 1145 uint64_t crc = -1ULL; 1146 int i; 1147 1148 ASSERT(zfs_crc64_table[128] == ZFS_CRC64_POLY); 1149 1150 for (i = 0; i < sizeof (dva_t); i++) 1151 crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ vdva[i]) & 0xFF]; 1152 1153 crc ^= (spa>>8) ^ birth; 1154 1155 return (crc); 1156} 1157 1158#define BUF_EMPTY(buf) \ 1159 ((buf)->b_dva.dva_word[0] == 0 && \ 1160 (buf)->b_dva.dva_word[1] == 0) 1161 1162#define BUF_EQUAL(spa, dva, birth, buf) \ 1163 ((buf)->b_dva.dva_word[0] == (dva)->dva_word[0]) && \ 1164 ((buf)->b_dva.dva_word[1] == (dva)->dva_word[1]) && \ 1165 ((buf)->b_birth == birth) && ((buf)->b_spa == spa) 1166 1167static void 1168buf_discard_identity(arc_buf_hdr_t *hdr) 1169{ 1170 hdr->b_dva.dva_word[0] = 0; 1171 hdr->b_dva.dva_word[1] = 0; 1172 hdr->b_birth = 0; 1173} 1174 1175static arc_buf_hdr_t * 1176buf_hash_find(uint64_t spa, const blkptr_t *bp, kmutex_t **lockp) 1177{ 1178 const dva_t *dva = BP_IDENTITY(bp); 1179 uint64_t birth = BP_PHYSICAL_BIRTH(bp); 1180 uint64_t idx = BUF_HASH_INDEX(spa, dva, birth); 1181 kmutex_t *hash_lock = BUF_HASH_LOCK(idx); 1182 arc_buf_hdr_t *hdr; 1183 1184 mutex_enter(hash_lock); 1185 for (hdr = buf_hash_table.ht_table[idx]; hdr != NULL; 1186 hdr = hdr->b_hash_next) { 1187 if (BUF_EQUAL(spa, dva, birth, hdr)) { 1188 *lockp = hash_lock; 1189 return (hdr); 1190 } 1191 } 1192 mutex_exit(hash_lock); 1193 *lockp = NULL; 1194 return (NULL); 1195} 1196 1197/* 1198 * Insert an entry into the hash table. If there is already an element 1199 * equal to elem in the hash table, then the already existing element 1200 * will be returned and the new element will not be inserted. 1201 * Otherwise returns NULL. 1202 * If lockp == NULL, the caller is assumed to already hold the hash lock. 1203 */ 1204static arc_buf_hdr_t * 1205buf_hash_insert(arc_buf_hdr_t *hdr, kmutex_t **lockp) 1206{ 1207 uint64_t idx = BUF_HASH_INDEX(hdr->b_spa, &hdr->b_dva, hdr->b_birth); 1208 kmutex_t *hash_lock = BUF_HASH_LOCK(idx); 1209 arc_buf_hdr_t *fhdr; 1210 uint32_t i; 1211 1212 ASSERT(!DVA_IS_EMPTY(&hdr->b_dva)); 1213 ASSERT(hdr->b_birth != 0); 1214 ASSERT(!HDR_IN_HASH_TABLE(hdr)); 1215 1216 if (lockp != NULL) { 1217 *lockp = hash_lock; 1218 mutex_enter(hash_lock); 1219 } else { 1220 ASSERT(MUTEX_HELD(hash_lock)); 1221 } 1222 1223 for (fhdr = buf_hash_table.ht_table[idx], i = 0; fhdr != NULL; 1224 fhdr = fhdr->b_hash_next, i++) { 1225 if (BUF_EQUAL(hdr->b_spa, &hdr->b_dva, hdr->b_birth, fhdr)) 1226 return (fhdr); 1227 } 1228 1229 hdr->b_hash_next = buf_hash_table.ht_table[idx]; 1230 buf_hash_table.ht_table[idx] = hdr; 1231 hdr->b_flags |= ARC_FLAG_IN_HASH_TABLE; 1232 1233 /* collect some hash table performance data */ 1234 if (i > 0) { 1235 ARCSTAT_BUMP(arcstat_hash_collisions); 1236 if (i == 1) 1237 ARCSTAT_BUMP(arcstat_hash_chains); 1238 1239 ARCSTAT_MAX(arcstat_hash_chain_max, i); 1240 } 1241 1242 ARCSTAT_BUMP(arcstat_hash_elements); 1243 ARCSTAT_MAXSTAT(arcstat_hash_elements); 1244 1245 return (NULL); 1246} 1247 1248static void 1249buf_hash_remove(arc_buf_hdr_t *hdr) 1250{ 1251 arc_buf_hdr_t *fhdr, **hdrp; 1252 uint64_t idx = BUF_HASH_INDEX(hdr->b_spa, &hdr->b_dva, hdr->b_birth); 1253 1254 ASSERT(MUTEX_HELD(BUF_HASH_LOCK(idx))); 1255 ASSERT(HDR_IN_HASH_TABLE(hdr)); 1256 1257 hdrp = &buf_hash_table.ht_table[idx]; 1258 while ((fhdr = *hdrp) != hdr) { 1259 ASSERT(fhdr != NULL); 1260 hdrp = &fhdr->b_hash_next; 1261 } 1262 *hdrp = hdr->b_hash_next; 1263 hdr->b_hash_next = NULL; 1264 hdr->b_flags &= ~ARC_FLAG_IN_HASH_TABLE; 1265 1266 /* collect some hash table performance data */ 1267 ARCSTAT_BUMPDOWN(arcstat_hash_elements); 1268 1269 if (buf_hash_table.ht_table[idx] && 1270 buf_hash_table.ht_table[idx]->b_hash_next == NULL) 1271 ARCSTAT_BUMPDOWN(arcstat_hash_chains); 1272} 1273 1274/* 1275 * Global data structures and functions for the buf kmem cache. 1276 */ 1277static kmem_cache_t *hdr_full_cache; 1278static kmem_cache_t *hdr_l2only_cache; 1279static kmem_cache_t *buf_cache; 1280 1281static void 1282buf_fini(void) 1283{ 1284 int i; 1285 1286 kmem_free(buf_hash_table.ht_table, 1287 (buf_hash_table.ht_mask + 1) * sizeof (void *)); 1288 for (i = 0; i < BUF_LOCKS; i++) 1289 mutex_destroy(&buf_hash_table.ht_locks[i].ht_lock); 1290 kmem_cache_destroy(hdr_full_cache); 1291 kmem_cache_destroy(hdr_l2only_cache); 1292 kmem_cache_destroy(buf_cache); 1293} 1294 1295/* 1296 * Constructor callback - called when the cache is empty 1297 * and a new buf is requested. 1298 */ 1299/* ARGSUSED */ 1300static int 1301hdr_full_cons(void *vbuf, void *unused, int kmflag) 1302{ 1303 arc_buf_hdr_t *hdr = vbuf; 1304 1305 bzero(hdr, HDR_FULL_SIZE); 1306 cv_init(&hdr->b_l1hdr.b_cv, NULL, CV_DEFAULT, NULL); 1307 refcount_create(&hdr->b_l1hdr.b_refcnt); 1308 mutex_init(&hdr->b_l1hdr.b_freeze_lock, NULL, MUTEX_DEFAULT, NULL); 1309 multilist_link_init(&hdr->b_l1hdr.b_arc_node); 1310 arc_space_consume(HDR_FULL_SIZE, ARC_SPACE_HDRS); 1311 1312 return (0); 1313} 1314 1315/* ARGSUSED */ 1316static int 1317hdr_l2only_cons(void *vbuf, void *unused, int kmflag) 1318{ 1319 arc_buf_hdr_t *hdr = vbuf; 1320 1321 bzero(hdr, HDR_L2ONLY_SIZE); 1322 arc_space_consume(HDR_L2ONLY_SIZE, ARC_SPACE_L2HDRS); 1323 1324 return (0); 1325} 1326 1327/* ARGSUSED */ 1328static int 1329buf_cons(void *vbuf, void *unused, int kmflag) 1330{ 1331 arc_buf_t *buf = vbuf; 1332 1333 bzero(buf, sizeof (arc_buf_t)); 1334 mutex_init(&buf->b_evict_lock, NULL, MUTEX_DEFAULT, NULL); 1335 arc_space_consume(sizeof (arc_buf_t), ARC_SPACE_HDRS); 1336 1337 return (0); 1338} 1339 1340/* 1341 * Destructor callback - called when a cached buf is 1342 * no longer required. 1343 */ 1344/* ARGSUSED */ 1345static void 1346hdr_full_dest(void *vbuf, void *unused) 1347{ 1348 arc_buf_hdr_t *hdr = vbuf; 1349 1350 ASSERT(BUF_EMPTY(hdr)); 1351 cv_destroy(&hdr->b_l1hdr.b_cv); 1352 refcount_destroy(&hdr->b_l1hdr.b_refcnt); 1353 mutex_destroy(&hdr->b_l1hdr.b_freeze_lock); 1354 ASSERT(!multilist_link_active(&hdr->b_l1hdr.b_arc_node)); 1355 arc_space_return(HDR_FULL_SIZE, ARC_SPACE_HDRS); 1356} 1357 1358/* ARGSUSED */ 1359static void 1360hdr_l2only_dest(void *vbuf, void *unused) 1361{ 1362 arc_buf_hdr_t *hdr = vbuf; 1363 1364 ASSERT(BUF_EMPTY(hdr)); 1365 arc_space_return(HDR_L2ONLY_SIZE, ARC_SPACE_L2HDRS); 1366} 1367 1368/* ARGSUSED */ 1369static void 1370buf_dest(void *vbuf, void *unused) 1371{ 1372 arc_buf_t *buf = vbuf; 1373 1374 mutex_destroy(&buf->b_evict_lock); 1375 arc_space_return(sizeof (arc_buf_t), ARC_SPACE_HDRS); 1376} 1377 1378/* 1379 * Reclaim callback -- invoked when memory is low. 1380 */ 1381/* ARGSUSED */ 1382static void 1383hdr_recl(void *unused) 1384{ 1385 dprintf("hdr_recl called\n"); 1386 /* 1387 * umem calls the reclaim func when we destroy the buf cache, 1388 * which is after we do arc_fini(). 1389 */ 1390 if (!arc_dead) 1391 cv_signal(&arc_reclaim_thread_cv); 1392} 1393 1394static void 1395buf_init(void) 1396{ 1397 uint64_t *ct; 1398 uint64_t hsize = 1ULL << 12; 1399 int i, j; 1400 1401 /* 1402 * The hash table is big enough to fill all of physical memory 1403 * with an average block size of zfs_arc_average_blocksize (default 8K). 1404 * By default, the table will take up 1405 * totalmem * sizeof(void*) / 8K (1MB per GB with 8-byte pointers). 1406 */ 1407 while (hsize * zfs_arc_average_blocksize < (uint64_t)physmem * PAGESIZE) 1408 hsize <<= 1; 1409retry: 1410 buf_hash_table.ht_mask = hsize - 1; 1411 buf_hash_table.ht_table = 1412 kmem_zalloc(hsize * sizeof (void*), KM_NOSLEEP); 1413 if (buf_hash_table.ht_table == NULL) { 1414 ASSERT(hsize > (1ULL << 8)); 1415 hsize >>= 1; 1416 goto retry; 1417 } 1418 1419 hdr_full_cache = kmem_cache_create("arc_buf_hdr_t_full", HDR_FULL_SIZE, 1420 0, hdr_full_cons, hdr_full_dest, hdr_recl, NULL, NULL, 0); 1421 hdr_l2only_cache = kmem_cache_create("arc_buf_hdr_t_l2only", 1422 HDR_L2ONLY_SIZE, 0, hdr_l2only_cons, hdr_l2only_dest, hdr_recl, 1423 NULL, NULL, 0); 1424 buf_cache = kmem_cache_create("arc_buf_t", sizeof (arc_buf_t), 1425 0, buf_cons, buf_dest, NULL, NULL, NULL, 0); 1426 1427 for (i = 0; i < 256; i++) 1428 for (ct = zfs_crc64_table + i, *ct = i, j = 8; j > 0; j--) 1429 *ct = (*ct >> 1) ^ (-(*ct & 1) & ZFS_CRC64_POLY); 1430 1431 for (i = 0; i < BUF_LOCKS; i++) { 1432 mutex_init(&buf_hash_table.ht_locks[i].ht_lock, 1433 NULL, MUTEX_DEFAULT, NULL); 1434 } 1435} 1436 1437/* 1438 * Transition between the two allocation states for the arc_buf_hdr struct. 1439 * The arc_buf_hdr struct can be allocated with (hdr_full_cache) or without 1440 * (hdr_l2only_cache) the fields necessary for the L1 cache - the smaller 1441 * version is used when a cache buffer is only in the L2ARC in order to reduce 1442 * memory usage. 1443 */ 1444static arc_buf_hdr_t * 1445arc_hdr_realloc(arc_buf_hdr_t *hdr, kmem_cache_t *old, kmem_cache_t *new) 1446{ 1447 ASSERT(HDR_HAS_L2HDR(hdr)); 1448 1449 arc_buf_hdr_t *nhdr; 1450 l2arc_dev_t *dev = hdr->b_l2hdr.b_dev; 1451 1452 ASSERT((old == hdr_full_cache && new == hdr_l2only_cache) || 1453 (old == hdr_l2only_cache && new == hdr_full_cache)); 1454 1455 nhdr = kmem_cache_alloc(new, KM_PUSHPAGE); 1456 1457 ASSERT(MUTEX_HELD(HDR_LOCK(hdr))); 1458 buf_hash_remove(hdr); 1459 1460 bcopy(hdr, nhdr, HDR_L2ONLY_SIZE); 1461 1462 if (new == hdr_full_cache) { 1463 nhdr->b_flags |= ARC_FLAG_HAS_L1HDR; 1464 /* 1465 * arc_access and arc_change_state need to be aware that a 1466 * header has just come out of L2ARC, so we set its state to 1467 * l2c_only even though it's about to change. 1468 */ 1469 nhdr->b_l1hdr.b_state = arc_l2c_only; 1470 1471 /* Verify previous threads set to NULL before freeing */ 1472 ASSERT3P(nhdr->b_l1hdr.b_tmp_cdata, ==, NULL); 1473 } else { 1474 ASSERT(hdr->b_l1hdr.b_buf == NULL); 1475 ASSERT0(hdr->b_l1hdr.b_datacnt); 1476 1477 /* 1478 * If we've reached here, We must have been called from 1479 * arc_evict_hdr(), as such we should have already been 1480 * removed from any ghost list we were previously on 1481 * (which protects us from racing with arc_evict_state), 1482 * thus no locking is needed during this check. 1483 */ 1484 ASSERT(!multilist_link_active(&hdr->b_l1hdr.b_arc_node)); 1485 1486 /* 1487 * A buffer must not be moved into the arc_l2c_only 1488 * state if it's not finished being written out to the 1489 * l2arc device. Otherwise, the b_l1hdr.b_tmp_cdata field 1490 * might try to be accessed, even though it was removed. 1491 */ 1492 VERIFY(!HDR_L2_WRITING(hdr)); 1493 VERIFY3P(hdr->b_l1hdr.b_tmp_cdata, ==, NULL); 1494 1495 nhdr->b_flags &= ~ARC_FLAG_HAS_L1HDR; 1496 } 1497 /* 1498 * The header has been reallocated so we need to re-insert it into any 1499 * lists it was on. 1500 */ 1501 (void) buf_hash_insert(nhdr, NULL); 1502 1503 ASSERT(list_link_active(&hdr->b_l2hdr.b_l2node)); 1504 1505 mutex_enter(&dev->l2ad_mtx); 1506 1507 /* 1508 * We must place the realloc'ed header back into the list at 1509 * the same spot. Otherwise, if it's placed earlier in the list, 1510 * l2arc_write_buffers() could find it during the function's 1511 * write phase, and try to write it out to the l2arc. 1512 */ 1513 list_insert_after(&dev->l2ad_buflist, hdr, nhdr); 1514 list_remove(&dev->l2ad_buflist, hdr); 1515 1516 mutex_exit(&dev->l2ad_mtx); 1517 1518 /* 1519 * Since we're using the pointer address as the tag when 1520 * incrementing and decrementing the l2ad_alloc refcount, we 1521 * must remove the old pointer (that we're about to destroy) and 1522 * add the new pointer to the refcount. Otherwise we'd remove 1523 * the wrong pointer address when calling arc_hdr_destroy() later. 1524 */ 1525 1526 (void) refcount_remove_many(&dev->l2ad_alloc, 1527 hdr->b_l2hdr.b_asize, hdr); 1528 1529 (void) refcount_add_many(&dev->l2ad_alloc, 1530 nhdr->b_l2hdr.b_asize, nhdr); 1531 1532 buf_discard_identity(hdr); 1533 hdr->b_freeze_cksum = NULL; 1534 kmem_cache_free(old, hdr); 1535 1536 return (nhdr); 1537} 1538 1539 1540#define ARC_MINTIME (hz>>4) /* 62 ms */ 1541 1542static void 1543arc_cksum_verify(arc_buf_t *buf) 1544{ 1545 zio_cksum_t zc; 1546 1547 if (!(zfs_flags & ZFS_DEBUG_MODIFY)) 1548 return; 1549 1550 mutex_enter(&buf->b_hdr->b_l1hdr.b_freeze_lock); 1551 if (buf->b_hdr->b_freeze_cksum == NULL || HDR_IO_ERROR(buf->b_hdr)) { 1552 mutex_exit(&buf->b_hdr->b_l1hdr.b_freeze_lock); 1553 return; 1554 } 1555 fletcher_2_native(buf->b_data, buf->b_hdr->b_size, &zc); 1556 if (!ZIO_CHECKSUM_EQUAL(*buf->b_hdr->b_freeze_cksum, zc)) 1557 panic("buffer modified while frozen!"); 1558 mutex_exit(&buf->b_hdr->b_l1hdr.b_freeze_lock); 1559} 1560 1561static int 1562arc_cksum_equal(arc_buf_t *buf) 1563{ 1564 zio_cksum_t zc; 1565 int equal; 1566 1567 mutex_enter(&buf->b_hdr->b_l1hdr.b_freeze_lock); 1568 fletcher_2_native(buf->b_data, buf->b_hdr->b_size, &zc); 1569 equal = ZIO_CHECKSUM_EQUAL(*buf->b_hdr->b_freeze_cksum, zc); 1570 mutex_exit(&buf->b_hdr->b_l1hdr.b_freeze_lock); 1571 1572 return (equal); 1573} 1574 1575static void 1576arc_cksum_compute(arc_buf_t *buf, boolean_t force) 1577{ 1578 if (!force && !(zfs_flags & ZFS_DEBUG_MODIFY)) 1579 return; 1580 1581 mutex_enter(&buf->b_hdr->b_l1hdr.b_freeze_lock); 1582 if (buf->b_hdr->b_freeze_cksum != NULL) { 1583 mutex_exit(&buf->b_hdr->b_l1hdr.b_freeze_lock); 1584 return; 1585 } 1586 buf->b_hdr->b_freeze_cksum = kmem_alloc(sizeof (zio_cksum_t), KM_SLEEP); 1587 fletcher_2_native(buf->b_data, buf->b_hdr->b_size, 1588 buf->b_hdr->b_freeze_cksum); 1589 mutex_exit(&buf->b_hdr->b_l1hdr.b_freeze_lock); 1590#ifdef illumos 1591 arc_buf_watch(buf); 1592#endif /* illumos */ 1593} 1594 1595#ifdef illumos 1596#ifndef _KERNEL 1597typedef struct procctl { 1598 long cmd; 1599 prwatch_t prwatch; 1600} procctl_t; 1601#endif 1602 1603/* ARGSUSED */ 1604static void 1605arc_buf_unwatch(arc_buf_t *buf) 1606{ 1607#ifndef _KERNEL 1608 if (arc_watch) { 1609 int result; 1610 procctl_t ctl; 1611 ctl.cmd = PCWATCH; 1612 ctl.prwatch.pr_vaddr = (uintptr_t)buf->b_data; 1613 ctl.prwatch.pr_size = 0; 1614 ctl.prwatch.pr_wflags = 0; 1615 result = write(arc_procfd, &ctl, sizeof (ctl)); 1616 ASSERT3U(result, ==, sizeof (ctl)); 1617 } 1618#endif 1619} 1620 1621/* ARGSUSED */ 1622static void 1623arc_buf_watch(arc_buf_t *buf) 1624{ 1625#ifndef _KERNEL 1626 if (arc_watch) { 1627 int result; 1628 procctl_t ctl; 1629 ctl.cmd = PCWATCH; 1630 ctl.prwatch.pr_vaddr = (uintptr_t)buf->b_data; 1631 ctl.prwatch.pr_size = buf->b_hdr->b_size; 1632 ctl.prwatch.pr_wflags = WA_WRITE; 1633 result = write(arc_procfd, &ctl, sizeof (ctl)); 1634 ASSERT3U(result, ==, sizeof (ctl)); 1635 } 1636#endif 1637} 1638#endif /* illumos */ 1639 1640static arc_buf_contents_t 1641arc_buf_type(arc_buf_hdr_t *hdr) 1642{ 1643 if (HDR_ISTYPE_METADATA(hdr)) { 1644 return (ARC_BUFC_METADATA); 1645 } else { 1646 return (ARC_BUFC_DATA); 1647 } 1648} 1649 1650static uint32_t 1651arc_bufc_to_flags(arc_buf_contents_t type) 1652{ 1653 switch (type) { 1654 case ARC_BUFC_DATA: 1655 /* metadata field is 0 if buffer contains normal data */ 1656 return (0); 1657 case ARC_BUFC_METADATA: 1658 return (ARC_FLAG_BUFC_METADATA); 1659 default: 1660 break; 1661 } 1662 panic("undefined ARC buffer type!"); 1663 return ((uint32_t)-1); 1664} 1665 1666void 1667arc_buf_thaw(arc_buf_t *buf) 1668{ 1669 if (zfs_flags & ZFS_DEBUG_MODIFY) { 1670 if (buf->b_hdr->b_l1hdr.b_state != arc_anon) 1671 panic("modifying non-anon buffer!"); 1672 if (HDR_IO_IN_PROGRESS(buf->b_hdr)) 1673 panic("modifying buffer while i/o in progress!"); 1674 arc_cksum_verify(buf); 1675 } 1676 1677 mutex_enter(&buf->b_hdr->b_l1hdr.b_freeze_lock); 1678 if (buf->b_hdr->b_freeze_cksum != NULL) { 1679 kmem_free(buf->b_hdr->b_freeze_cksum, sizeof (zio_cksum_t)); 1680 buf->b_hdr->b_freeze_cksum = NULL; 1681 } 1682 1683#ifdef ZFS_DEBUG 1684 if (zfs_flags & ZFS_DEBUG_MODIFY) { 1685 if (buf->b_hdr->b_l1hdr.b_thawed != NULL) 1686 kmem_free(buf->b_hdr->b_l1hdr.b_thawed, 1); 1687 buf->b_hdr->b_l1hdr.b_thawed = kmem_alloc(1, KM_SLEEP); 1688 } 1689#endif 1690 1691 mutex_exit(&buf->b_hdr->b_l1hdr.b_freeze_lock); 1692 1693#ifdef illumos 1694 arc_buf_unwatch(buf); 1695#endif /* illumos */ 1696} 1697 1698void 1699arc_buf_freeze(arc_buf_t *buf) 1700{ 1701 kmutex_t *hash_lock; 1702 1703 if (!(zfs_flags & ZFS_DEBUG_MODIFY)) 1704 return; 1705 1706 hash_lock = HDR_LOCK(buf->b_hdr); 1707 mutex_enter(hash_lock); 1708 1709 ASSERT(buf->b_hdr->b_freeze_cksum != NULL || 1710 buf->b_hdr->b_l1hdr.b_state == arc_anon); 1711 arc_cksum_compute(buf, B_FALSE); 1712 mutex_exit(hash_lock); 1713 1714} 1715 1716static void 1717add_reference(arc_buf_hdr_t *hdr, kmutex_t *hash_lock, void *tag) 1718{ 1719 ASSERT(HDR_HAS_L1HDR(hdr)); 1720 ASSERT(MUTEX_HELD(hash_lock)); 1721 arc_state_t *state = hdr->b_l1hdr.b_state; 1722 1723 if ((refcount_add(&hdr->b_l1hdr.b_refcnt, tag) == 1) && 1724 (state != arc_anon)) { 1725 /* We don't use the L2-only state list. */ 1726 if (state != arc_l2c_only) { 1727 arc_buf_contents_t type = arc_buf_type(hdr); 1728 uint64_t delta = hdr->b_size * hdr->b_l1hdr.b_datacnt; 1729 multilist_t *list = &state->arcs_list[type]; 1730 uint64_t *size = &state->arcs_lsize[type]; 1731 1732 multilist_remove(list, hdr); 1733 1734 if (GHOST_STATE(state)) { 1735 ASSERT0(hdr->b_l1hdr.b_datacnt); 1736 ASSERT3P(hdr->b_l1hdr.b_buf, ==, NULL); 1737 delta = hdr->b_size; 1738 } 1739 ASSERT(delta > 0); 1740 ASSERT3U(*size, >=, delta); 1741 atomic_add_64(size, -delta); 1742 } 1743 /* remove the prefetch flag if we get a reference */ 1744 hdr->b_flags &= ~ARC_FLAG_PREFETCH; 1745 } 1746} 1747 1748static int 1749remove_reference(arc_buf_hdr_t *hdr, kmutex_t *hash_lock, void *tag) 1750{ 1751 int cnt; 1752 arc_state_t *state = hdr->b_l1hdr.b_state; 1753 1754 ASSERT(HDR_HAS_L1HDR(hdr)); 1755 ASSERT(state == arc_anon || MUTEX_HELD(hash_lock)); 1756 ASSERT(!GHOST_STATE(state)); 1757 1758 /* 1759 * arc_l2c_only counts as a ghost state so we don't need to explicitly 1760 * check to prevent usage of the arc_l2c_only list. 1761 */ 1762 if (((cnt = refcount_remove(&hdr->b_l1hdr.b_refcnt, tag)) == 0) && 1763 (state != arc_anon)) { 1764 arc_buf_contents_t type = arc_buf_type(hdr); 1765 multilist_t *list = &state->arcs_list[type]; 1766 uint64_t *size = &state->arcs_lsize[type]; 1767 1768 multilist_insert(list, hdr); 1769 1770 ASSERT(hdr->b_l1hdr.b_datacnt > 0); 1771 atomic_add_64(size, hdr->b_size * 1772 hdr->b_l1hdr.b_datacnt); 1773 } 1774 return (cnt); 1775} 1776 1777/* 1778 * Move the supplied buffer to the indicated state. The hash lock 1779 * for the buffer must be held by the caller. 1780 */ 1781static void 1782arc_change_state(arc_state_t *new_state, arc_buf_hdr_t *hdr, 1783 kmutex_t *hash_lock) 1784{ 1785 arc_state_t *old_state; 1786 int64_t refcnt; 1787 uint32_t datacnt; 1788 uint64_t from_delta, to_delta; 1789 arc_buf_contents_t buftype = arc_buf_type(hdr); 1790 1791 /* 1792 * We almost always have an L1 hdr here, since we call arc_hdr_realloc() 1793 * in arc_read() when bringing a buffer out of the L2ARC. However, the 1794 * L1 hdr doesn't always exist when we change state to arc_anon before 1795 * destroying a header, in which case reallocating to add the L1 hdr is 1796 * pointless. 1797 */ 1798 if (HDR_HAS_L1HDR(hdr)) { 1799 old_state = hdr->b_l1hdr.b_state; 1800 refcnt = refcount_count(&hdr->b_l1hdr.b_refcnt); 1801 datacnt = hdr->b_l1hdr.b_datacnt; 1802 } else { 1803 old_state = arc_l2c_only; 1804 refcnt = 0; 1805 datacnt = 0; 1806 } 1807 1808 ASSERT(MUTEX_HELD(hash_lock)); 1809 ASSERT3P(new_state, !=, old_state); 1810 ASSERT(refcnt == 0 || datacnt > 0); 1811 ASSERT(!GHOST_STATE(new_state) || datacnt == 0); 1812 ASSERT(old_state != arc_anon || datacnt <= 1); 1813 1814 from_delta = to_delta = datacnt * hdr->b_size; 1815 1816 /* 1817 * If this buffer is evictable, transfer it from the 1818 * old state list to the new state list. 1819 */ 1820 if (refcnt == 0) { 1821 if (old_state != arc_anon && old_state != arc_l2c_only) { 1822 uint64_t *size = &old_state->arcs_lsize[buftype]; 1823 1824 ASSERT(HDR_HAS_L1HDR(hdr)); 1825 multilist_remove(&old_state->arcs_list[buftype], hdr); 1826 1827 /* 1828 * If prefetching out of the ghost cache, 1829 * we will have a non-zero datacnt. 1830 */ 1831 if (GHOST_STATE(old_state) && datacnt == 0) { 1832 /* ghost elements have a ghost size */ 1833 ASSERT(hdr->b_l1hdr.b_buf == NULL); 1834 from_delta = hdr->b_size; 1835 } 1836 ASSERT3U(*size, >=, from_delta); 1837 atomic_add_64(size, -from_delta); 1838 } 1839 if (new_state != arc_anon && new_state != arc_l2c_only) { 1840 uint64_t *size = &new_state->arcs_lsize[buftype]; 1841 1842 /* 1843 * An L1 header always exists here, since if we're 1844 * moving to some L1-cached state (i.e. not l2c_only or 1845 * anonymous), we realloc the header to add an L1hdr 1846 * beforehand. 1847 */ 1848 ASSERT(HDR_HAS_L1HDR(hdr)); 1849 multilist_insert(&new_state->arcs_list[buftype], hdr); 1850 1851 /* ghost elements have a ghost size */ 1852 if (GHOST_STATE(new_state)) { 1853 ASSERT0(datacnt); 1854 ASSERT(hdr->b_l1hdr.b_buf == NULL); 1855 to_delta = hdr->b_size; 1856 } 1857 atomic_add_64(size, to_delta); 1858 } 1859 } 1860 1861 ASSERT(!BUF_EMPTY(hdr)); 1862 if (new_state == arc_anon && HDR_IN_HASH_TABLE(hdr)) 1863 buf_hash_remove(hdr); 1864 1865 /* adjust state sizes (ignore arc_l2c_only) */ 1866 if (to_delta && new_state != arc_l2c_only) 1867 atomic_add_64(&new_state->arcs_size, to_delta); 1868 if (from_delta && old_state != arc_l2c_only) { 1869 ASSERT3U(old_state->arcs_size, >=, from_delta); 1870 atomic_add_64(&old_state->arcs_size, -from_delta); 1871 } 1872 if (HDR_HAS_L1HDR(hdr)) 1873 hdr->b_l1hdr.b_state = new_state; 1874 1875 /* 1876 * L2 headers should never be on the L2 state list since they don't 1877 * have L1 headers allocated. 1878 */ 1879 ASSERT(multilist_is_empty(&arc_l2c_only->arcs_list[ARC_BUFC_DATA]) && 1880 multilist_is_empty(&arc_l2c_only->arcs_list[ARC_BUFC_METADATA])); 1881} 1882 1883void 1884arc_space_consume(uint64_t space, arc_space_type_t type) 1885{ 1886 ASSERT(type >= 0 && type < ARC_SPACE_NUMTYPES); 1887 1888 switch (type) { 1889 case ARC_SPACE_DATA: 1890 ARCSTAT_INCR(arcstat_data_size, space); 1891 break; 1892 case ARC_SPACE_META: 1893 ARCSTAT_INCR(arcstat_metadata_size, space); 1894 break; 1895 case ARC_SPACE_OTHER: 1896 ARCSTAT_INCR(arcstat_other_size, space); 1897 break; 1898 case ARC_SPACE_HDRS: 1899 ARCSTAT_INCR(arcstat_hdr_size, space); 1900 break; 1901 case ARC_SPACE_L2HDRS: 1902 ARCSTAT_INCR(arcstat_l2_hdr_size, space); 1903 break; 1904 } 1905 1906 if (type != ARC_SPACE_DATA) 1907 ARCSTAT_INCR(arcstat_meta_used, space); 1908 1909 atomic_add_64(&arc_size, space); 1910} 1911 1912void 1913arc_space_return(uint64_t space, arc_space_type_t type) 1914{ 1915 ASSERT(type >= 0 && type < ARC_SPACE_NUMTYPES); 1916 1917 switch (type) { 1918 case ARC_SPACE_DATA: 1919 ARCSTAT_INCR(arcstat_data_size, -space); 1920 break; 1921 case ARC_SPACE_META: 1922 ARCSTAT_INCR(arcstat_metadata_size, -space); 1923 break; 1924 case ARC_SPACE_OTHER: 1925 ARCSTAT_INCR(arcstat_other_size, -space); 1926 break; 1927 case ARC_SPACE_HDRS: 1928 ARCSTAT_INCR(arcstat_hdr_size, -space); 1929 break; 1930 case ARC_SPACE_L2HDRS: 1931 ARCSTAT_INCR(arcstat_l2_hdr_size, -space); 1932 break; 1933 } 1934 1935 if (type != ARC_SPACE_DATA) { 1936 ASSERT(arc_meta_used >= space); 1937 if (arc_meta_max < arc_meta_used) 1938 arc_meta_max = arc_meta_used; 1939 ARCSTAT_INCR(arcstat_meta_used, -space); 1940 } 1941 1942 ASSERT(arc_size >= space); 1943 atomic_add_64(&arc_size, -space); 1944} 1945 1946arc_buf_t * 1947arc_buf_alloc(spa_t *spa, int32_t size, void *tag, arc_buf_contents_t type) 1948{ 1949 arc_buf_hdr_t *hdr; 1950 arc_buf_t *buf; 1951 1952 ASSERT3U(size, >, 0); 1953 hdr = kmem_cache_alloc(hdr_full_cache, KM_PUSHPAGE); 1954 ASSERT(BUF_EMPTY(hdr)); 1955 ASSERT3P(hdr->b_freeze_cksum, ==, NULL); 1956 hdr->b_size = size; 1957 hdr->b_spa = spa_load_guid(spa); 1958 1959 buf = kmem_cache_alloc(buf_cache, KM_PUSHPAGE); 1960 buf->b_hdr = hdr; 1961 buf->b_data = NULL; 1962 buf->b_efunc = NULL; 1963 buf->b_private = NULL; 1964 buf->b_next = NULL; 1965 1966 hdr->b_flags = arc_bufc_to_flags(type); 1967 hdr->b_flags |= ARC_FLAG_HAS_L1HDR; 1968 1969 hdr->b_l1hdr.b_buf = buf; 1970 hdr->b_l1hdr.b_state = arc_anon; 1971 hdr->b_l1hdr.b_arc_access = 0; 1972 hdr->b_l1hdr.b_datacnt = 1; 1973 hdr->b_l1hdr.b_tmp_cdata = NULL; 1974 1975 arc_get_data_buf(buf); 1976 ASSERT(refcount_is_zero(&hdr->b_l1hdr.b_refcnt)); 1977 (void) refcount_add(&hdr->b_l1hdr.b_refcnt, tag); 1978 1979 return (buf); 1980} 1981 1982static char *arc_onloan_tag = "onloan"; 1983 1984/* 1985 * Loan out an anonymous arc buffer. Loaned buffers are not counted as in 1986 * flight data by arc_tempreserve_space() until they are "returned". Loaned 1987 * buffers must be returned to the arc before they can be used by the DMU or 1988 * freed. 1989 */ 1990arc_buf_t * 1991arc_loan_buf(spa_t *spa, int size) 1992{ 1993 arc_buf_t *buf; 1994 1995 buf = arc_buf_alloc(spa, size, arc_onloan_tag, ARC_BUFC_DATA); 1996 1997 atomic_add_64(&arc_loaned_bytes, size); 1998 return (buf); 1999} 2000 2001/* 2002 * Return a loaned arc buffer to the arc. 2003 */ 2004void 2005arc_return_buf(arc_buf_t *buf, void *tag) 2006{ 2007 arc_buf_hdr_t *hdr = buf->b_hdr; 2008 2009 ASSERT(buf->b_data != NULL); 2010 ASSERT(HDR_HAS_L1HDR(hdr)); 2011 (void) refcount_add(&hdr->b_l1hdr.b_refcnt, tag); 2012 (void) refcount_remove(&hdr->b_l1hdr.b_refcnt, arc_onloan_tag); 2013 2014 atomic_add_64(&arc_loaned_bytes, -hdr->b_size); 2015} 2016 2017/* Detach an arc_buf from a dbuf (tag) */ 2018void 2019arc_loan_inuse_buf(arc_buf_t *buf, void *tag) 2020{ 2021 arc_buf_hdr_t *hdr = buf->b_hdr; 2022 2023 ASSERT(buf->b_data != NULL); 2024 ASSERT(HDR_HAS_L1HDR(hdr)); 2025 (void) refcount_add(&hdr->b_l1hdr.b_refcnt, arc_onloan_tag); 2026 (void) refcount_remove(&hdr->b_l1hdr.b_refcnt, tag); 2027 buf->b_efunc = NULL; 2028 buf->b_private = NULL; 2029 2030 atomic_add_64(&arc_loaned_bytes, hdr->b_size); 2031} 2032 2033static arc_buf_t * 2034arc_buf_clone(arc_buf_t *from) 2035{ 2036 arc_buf_t *buf; 2037 arc_buf_hdr_t *hdr = from->b_hdr; 2038 uint64_t size = hdr->b_size; 2039 2040 ASSERT(HDR_HAS_L1HDR(hdr)); 2041 ASSERT(hdr->b_l1hdr.b_state != arc_anon); 2042 2043 buf = kmem_cache_alloc(buf_cache, KM_PUSHPAGE); 2044 buf->b_hdr = hdr; 2045 buf->b_data = NULL; 2046 buf->b_efunc = NULL; 2047 buf->b_private = NULL; 2048 buf->b_next = hdr->b_l1hdr.b_buf; 2049 hdr->b_l1hdr.b_buf = buf; 2050 arc_get_data_buf(buf); 2051 bcopy(from->b_data, buf->b_data, size); 2052 2053 /* 2054 * This buffer already exists in the arc so create a duplicate 2055 * copy for the caller. If the buffer is associated with user data 2056 * then track the size and number of duplicates. These stats will be 2057 * updated as duplicate buffers are created and destroyed. 2058 */ 2059 if (HDR_ISTYPE_DATA(hdr)) { 2060 ARCSTAT_BUMP(arcstat_duplicate_buffers); 2061 ARCSTAT_INCR(arcstat_duplicate_buffers_size, size); 2062 } 2063 hdr->b_l1hdr.b_datacnt += 1; 2064 return (buf); 2065} 2066 2067void 2068arc_buf_add_ref(arc_buf_t *buf, void* tag) 2069{ 2070 arc_buf_hdr_t *hdr; 2071 kmutex_t *hash_lock; 2072 2073 /* 2074 * Check to see if this buffer is evicted. Callers 2075 * must verify b_data != NULL to know if the add_ref 2076 * was successful. 2077 */ 2078 mutex_enter(&buf->b_evict_lock); 2079 if (buf->b_data == NULL) { 2080 mutex_exit(&buf->b_evict_lock); 2081 return; 2082 } 2083 hash_lock = HDR_LOCK(buf->b_hdr); 2084 mutex_enter(hash_lock); 2085 hdr = buf->b_hdr; 2086 ASSERT(HDR_HAS_L1HDR(hdr)); 2087 ASSERT3P(hash_lock, ==, HDR_LOCK(hdr)); 2088 mutex_exit(&buf->b_evict_lock); 2089 2090 ASSERT(hdr->b_l1hdr.b_state == arc_mru || 2091 hdr->b_l1hdr.b_state == arc_mfu); 2092 2093 add_reference(hdr, hash_lock, tag); 2094 DTRACE_PROBE1(arc__hit, arc_buf_hdr_t *, hdr); 2095 arc_access(hdr, hash_lock); 2096 mutex_exit(hash_lock); 2097 ARCSTAT_BUMP(arcstat_hits); 2098 ARCSTAT_CONDSTAT(!HDR_PREFETCH(hdr), 2099 demand, prefetch, !HDR_ISTYPE_METADATA(hdr), 2100 data, metadata, hits); 2101} 2102 2103static void 2104arc_buf_free_on_write(void *data, size_t size, 2105 void (*free_func)(void *, size_t)) 2106{ 2107 l2arc_data_free_t *df; 2108 2109 df = kmem_alloc(sizeof (*df), KM_SLEEP); 2110 df->l2df_data = data; 2111 df->l2df_size = size; 2112 df->l2df_func = free_func; 2113 mutex_enter(&l2arc_free_on_write_mtx); 2114 list_insert_head(l2arc_free_on_write, df); 2115 mutex_exit(&l2arc_free_on_write_mtx); 2116} 2117 2118/* 2119 * Free the arc data buffer. If it is an l2arc write in progress, 2120 * the buffer is placed on l2arc_free_on_write to be freed later. 2121 */ 2122static void 2123arc_buf_data_free(arc_buf_t *buf, void (*free_func)(void *, size_t)) 2124{ 2125 arc_buf_hdr_t *hdr = buf->b_hdr; 2126 2127 if (HDR_L2_WRITING(hdr)) { 2128 arc_buf_free_on_write(buf->b_data, hdr->b_size, free_func); 2129 ARCSTAT_BUMP(arcstat_l2_free_on_write); 2130 } else { 2131 free_func(buf->b_data, hdr->b_size); 2132 } 2133} 2134 2135/* 2136 * Free up buf->b_data and if 'remove' is set, then pull the 2137 * arc_buf_t off of the the arc_buf_hdr_t's list and free it. 2138 */ 2139static void 2140arc_buf_l2_cdata_free(arc_buf_hdr_t *hdr) 2141{ 2142 ASSERT(HDR_HAS_L2HDR(hdr)); 2143 ASSERT(MUTEX_HELD(&hdr->b_l2hdr.b_dev->l2ad_mtx)); 2144 2145 /* 2146 * The b_tmp_cdata field is linked off of the b_l1hdr, so if 2147 * that doesn't exist, the header is in the arc_l2c_only state, 2148 * and there isn't anything to free (it's already been freed). 2149 */ 2150 if (!HDR_HAS_L1HDR(hdr)) 2151 return; 2152 2153 /* 2154 * The header isn't being written to the l2arc device, thus it 2155 * shouldn't have a b_tmp_cdata to free. 2156 */ 2157 if (!HDR_L2_WRITING(hdr)) { 2158 ASSERT3P(hdr->b_l1hdr.b_tmp_cdata, ==, NULL); 2159 return; 2160 } 2161 2162 /* 2163 * The header does not have compression enabled. This can be due 2164 * to the buffer not being compressible, or because we're 2165 * freeing the buffer before the second phase of 2166 * l2arc_write_buffer() has started (which does the compression 2167 * step). In either case, b_tmp_cdata does not point to a 2168 * separately compressed buffer, so there's nothing to free (it 2169 * points to the same buffer as the arc_buf_t's b_data field). 2170 */ 2171 if (HDR_GET_COMPRESS(hdr) == ZIO_COMPRESS_OFF) { 2172 hdr->b_l1hdr.b_tmp_cdata = NULL; 2173 return; 2174 } 2175 2176 /* 2177 * There's nothing to free since the buffer was all zero's and 2178 * compressed to a zero length buffer. 2179 */ 2180 if (HDR_GET_COMPRESS(hdr) == ZIO_COMPRESS_EMPTY) { 2181 ASSERT3P(hdr->b_l1hdr.b_tmp_cdata, ==, NULL); 2182 return; 2183 } 2184 2185 ASSERT(L2ARC_IS_VALID_COMPRESS(HDR_GET_COMPRESS(hdr))); 2186 2187 arc_buf_free_on_write(hdr->b_l1hdr.b_tmp_cdata, 2188 hdr->b_size, zio_data_buf_free); 2189 2190 ARCSTAT_BUMP(arcstat_l2_cdata_free_on_write); 2191 hdr->b_l1hdr.b_tmp_cdata = NULL; 2192} 2193 2194static void 2195arc_buf_destroy(arc_buf_t *buf, boolean_t remove) 2196{ 2197 arc_buf_t **bufp; 2198 2199 /* free up data associated with the buf */ 2200 if (buf->b_data != NULL) { 2201 arc_state_t *state = buf->b_hdr->b_l1hdr.b_state; 2202 uint64_t size = buf->b_hdr->b_size; 2203 arc_buf_contents_t type = arc_buf_type(buf->b_hdr); 2204 2205 arc_cksum_verify(buf); 2206#ifdef illumos 2207 arc_buf_unwatch(buf); 2208#endif /* illumos */ 2209 2210 if (type == ARC_BUFC_METADATA) { 2211 arc_buf_data_free(buf, zio_buf_free); 2212 arc_space_return(size, ARC_SPACE_META); 2213 } else { 2214 ASSERT(type == ARC_BUFC_DATA); 2215 arc_buf_data_free(buf, zio_data_buf_free); 2216 arc_space_return(size, ARC_SPACE_DATA); 2217 } 2218 2219 /* protected by hash lock, if in the hash table */ 2220 if (multilist_link_active(&buf->b_hdr->b_l1hdr.b_arc_node)) { 2221 uint64_t *cnt = &state->arcs_lsize[type]; 2222 2223 ASSERT(refcount_is_zero( 2224 &buf->b_hdr->b_l1hdr.b_refcnt)); 2225 ASSERT(state != arc_anon && state != arc_l2c_only); 2226 2227 ASSERT3U(*cnt, >=, size); 2228 atomic_add_64(cnt, -size); 2229 } 2230 ASSERT3U(state->arcs_size, >=, size); 2231 atomic_add_64(&state->arcs_size, -size); 2232 buf->b_data = NULL; 2233 2234 /* 2235 * If we're destroying a duplicate buffer make sure 2236 * that the appropriate statistics are updated. 2237 */ 2238 if (buf->b_hdr->b_l1hdr.b_datacnt > 1 && 2239 HDR_ISTYPE_DATA(buf->b_hdr)) { 2240 ARCSTAT_BUMPDOWN(arcstat_duplicate_buffers); 2241 ARCSTAT_INCR(arcstat_duplicate_buffers_size, -size); 2242 } 2243 ASSERT(buf->b_hdr->b_l1hdr.b_datacnt > 0); 2244 buf->b_hdr->b_l1hdr.b_datacnt -= 1; 2245 } 2246 2247 /* only remove the buf if requested */ 2248 if (!remove) 2249 return; 2250 2251 /* remove the buf from the hdr list */ 2252 for (bufp = &buf->b_hdr->b_l1hdr.b_buf; *bufp != buf; 2253 bufp = &(*bufp)->b_next) 2254 continue; 2255 *bufp = buf->b_next; 2256 buf->b_next = NULL; 2257 2258 ASSERT(buf->b_efunc == NULL); 2259 2260 /* clean up the buf */ 2261 buf->b_hdr = NULL; 2262 kmem_cache_free(buf_cache, buf); 2263} 2264 2265static void 2266arc_hdr_l2hdr_destroy(arc_buf_hdr_t *hdr) 2267{ 2268 l2arc_buf_hdr_t *l2hdr = &hdr->b_l2hdr; 2269 l2arc_dev_t *dev = l2hdr->b_dev; 2270 2271 ASSERT(MUTEX_HELD(&dev->l2ad_mtx)); 2272 ASSERT(HDR_HAS_L2HDR(hdr)); 2273 2274 list_remove(&dev->l2ad_buflist, hdr); 2275 2276 /* 2277 * We don't want to leak the b_tmp_cdata buffer that was 2278 * allocated in l2arc_write_buffers() 2279 */ 2280 arc_buf_l2_cdata_free(hdr); 2281 2282 /* 2283 * If the l2hdr's b_daddr is equal to L2ARC_ADDR_UNSET, then 2284 * this header is being processed by l2arc_write_buffers() (i.e. 2285 * it's in the first stage of l2arc_write_buffers()). 2286 * Re-affirming that truth here, just to serve as a reminder. If 2287 * b_daddr does not equal L2ARC_ADDR_UNSET, then the header may or 2288 * may not have its HDR_L2_WRITING flag set. (the write may have 2289 * completed, in which case HDR_L2_WRITING will be false and the 2290 * b_daddr field will point to the address of the buffer on disk). 2291 */ 2292 IMPLY(l2hdr->b_daddr == L2ARC_ADDR_UNSET, HDR_L2_WRITING(hdr)); 2293 2294 /* 2295 * If b_daddr is equal to L2ARC_ADDR_UNSET, we're racing with 2296 * l2arc_write_buffers(). Since we've just removed this header 2297 * from the l2arc buffer list, this header will never reach the 2298 * second stage of l2arc_write_buffers(), which increments the 2299 * accounting stats for this header. Thus, we must be careful 2300 * not to decrement them for this header either. 2301 */ 2302 if (l2hdr->b_daddr != L2ARC_ADDR_UNSET) { 2303 ARCSTAT_INCR(arcstat_l2_asize, -l2hdr->b_asize); 2304 ARCSTAT_INCR(arcstat_l2_size, -hdr->b_size); 2305 2306 vdev_space_update(dev->l2ad_vdev, 2307 -l2hdr->b_asize, 0, 0); 2308 2309 (void) refcount_remove_many(&dev->l2ad_alloc, 2310 l2hdr->b_asize, hdr); 2311 } 2312 2313 hdr->b_flags &= ~ARC_FLAG_HAS_L2HDR; 2314} 2315 2316static void 2317arc_hdr_destroy(arc_buf_hdr_t *hdr) 2318{ 2319 if (HDR_HAS_L1HDR(hdr)) { 2320 ASSERT(hdr->b_l1hdr.b_buf == NULL || 2321 hdr->b_l1hdr.b_datacnt > 0); 2322 ASSERT(refcount_is_zero(&hdr->b_l1hdr.b_refcnt)); 2323 ASSERT3P(hdr->b_l1hdr.b_state, ==, arc_anon); 2324 } 2325 ASSERT(!HDR_IO_IN_PROGRESS(hdr)); 2326 ASSERT(!HDR_IN_HASH_TABLE(hdr)); 2327 2328 if (HDR_HAS_L2HDR(hdr)) { 2329 l2arc_dev_t *dev = hdr->b_l2hdr.b_dev; 2330 boolean_t buflist_held = MUTEX_HELD(&dev->l2ad_mtx); 2331 2332 if (!buflist_held) 2333 mutex_enter(&dev->l2ad_mtx); 2334 2335 /* 2336 * Even though we checked this conditional above, we 2337 * need to check this again now that we have the 2338 * l2ad_mtx. This is because we could be racing with 2339 * another thread calling l2arc_evict() which might have 2340 * destroyed this header's L2 portion as we were waiting 2341 * to acquire the l2ad_mtx. If that happens, we don't 2342 * want to re-destroy the header's L2 portion. 2343 */ 2344 if (HDR_HAS_L2HDR(hdr)) { 2345 if (hdr->b_l2hdr.b_daddr != L2ARC_ADDR_UNSET) 2346 trim_map_free(dev->l2ad_vdev, 2347 hdr->b_l2hdr.b_daddr, 2348 hdr->b_l2hdr.b_asize, 0); 2349 arc_hdr_l2hdr_destroy(hdr); 2350 } 2351 2352 if (!buflist_held) 2353 mutex_exit(&dev->l2ad_mtx); 2354 } 2355 2356 if (!BUF_EMPTY(hdr)) 2357 buf_discard_identity(hdr); 2358 if (hdr->b_freeze_cksum != NULL) { 2359 kmem_free(hdr->b_freeze_cksum, sizeof (zio_cksum_t)); 2360 hdr->b_freeze_cksum = NULL; 2361 } 2362 2363 if (HDR_HAS_L1HDR(hdr)) { 2364 while (hdr->b_l1hdr.b_buf) { 2365 arc_buf_t *buf = hdr->b_l1hdr.b_buf; 2366 2367 if (buf->b_efunc != NULL) { 2368 mutex_enter(&arc_user_evicts_lock); 2369 mutex_enter(&buf->b_evict_lock); 2370 ASSERT(buf->b_hdr != NULL); 2371 arc_buf_destroy(hdr->b_l1hdr.b_buf, FALSE); 2372 hdr->b_l1hdr.b_buf = buf->b_next; 2373 buf->b_hdr = &arc_eviction_hdr; 2374 buf->b_next = arc_eviction_list; 2375 arc_eviction_list = buf; 2376 mutex_exit(&buf->b_evict_lock); 2377 cv_signal(&arc_user_evicts_cv); 2378 mutex_exit(&arc_user_evicts_lock); 2379 } else { 2380 arc_buf_destroy(hdr->b_l1hdr.b_buf, TRUE); 2381 } 2382 } 2383#ifdef ZFS_DEBUG 2384 if (hdr->b_l1hdr.b_thawed != NULL) { 2385 kmem_free(hdr->b_l1hdr.b_thawed, 1); 2386 hdr->b_l1hdr.b_thawed = NULL; 2387 } 2388#endif 2389 } 2390 2391 ASSERT3P(hdr->b_hash_next, ==, NULL); 2392 if (HDR_HAS_L1HDR(hdr)) { 2393 ASSERT(!multilist_link_active(&hdr->b_l1hdr.b_arc_node)); 2394 ASSERT3P(hdr->b_l1hdr.b_acb, ==, NULL); 2395 kmem_cache_free(hdr_full_cache, hdr); 2396 } else { 2397 kmem_cache_free(hdr_l2only_cache, hdr); 2398 } 2399} 2400 2401void 2402arc_buf_free(arc_buf_t *buf, void *tag) 2403{ 2404 arc_buf_hdr_t *hdr = buf->b_hdr; 2405 int hashed = hdr->b_l1hdr.b_state != arc_anon; 2406 2407 ASSERT(buf->b_efunc == NULL); 2408 ASSERT(buf->b_data != NULL); 2409 2410 if (hashed) { 2411 kmutex_t *hash_lock = HDR_LOCK(hdr); 2412 2413 mutex_enter(hash_lock); 2414 hdr = buf->b_hdr; 2415 ASSERT3P(hash_lock, ==, HDR_LOCK(hdr)); 2416 2417 (void) remove_reference(hdr, hash_lock, tag); 2418 if (hdr->b_l1hdr.b_datacnt > 1) { 2419 arc_buf_destroy(buf, TRUE); 2420 } else { 2421 ASSERT(buf == hdr->b_l1hdr.b_buf); 2422 ASSERT(buf->b_efunc == NULL); 2423 hdr->b_flags |= ARC_FLAG_BUF_AVAILABLE; 2424 } 2425 mutex_exit(hash_lock); 2426 } else if (HDR_IO_IN_PROGRESS(hdr)) { 2427 int destroy_hdr; 2428 /* 2429 * We are in the middle of an async write. Don't destroy 2430 * this buffer unless the write completes before we finish 2431 * decrementing the reference count. 2432 */ 2433 mutex_enter(&arc_user_evicts_lock); 2434 (void) remove_reference(hdr, NULL, tag); 2435 ASSERT(refcount_is_zero(&hdr->b_l1hdr.b_refcnt)); 2436 destroy_hdr = !HDR_IO_IN_PROGRESS(hdr); 2437 mutex_exit(&arc_user_evicts_lock); 2438 if (destroy_hdr) 2439 arc_hdr_destroy(hdr); 2440 } else { 2441 if (remove_reference(hdr, NULL, tag) > 0) 2442 arc_buf_destroy(buf, TRUE); 2443 else 2444 arc_hdr_destroy(hdr); 2445 } 2446} 2447 2448boolean_t 2449arc_buf_remove_ref(arc_buf_t *buf, void* tag) 2450{ 2451 arc_buf_hdr_t *hdr = buf->b_hdr; 2452 kmutex_t *hash_lock = HDR_LOCK(hdr); 2453 boolean_t no_callback = (buf->b_efunc == NULL); 2454 2455 if (hdr->b_l1hdr.b_state == arc_anon) { 2456 ASSERT(hdr->b_l1hdr.b_datacnt == 1); 2457 arc_buf_free(buf, tag); 2458 return (no_callback); 2459 } 2460 2461 mutex_enter(hash_lock); 2462 hdr = buf->b_hdr; 2463 ASSERT(hdr->b_l1hdr.b_datacnt > 0); 2464 ASSERT3P(hash_lock, ==, HDR_LOCK(hdr)); 2465 ASSERT(hdr->b_l1hdr.b_state != arc_anon); 2466 ASSERT(buf->b_data != NULL); 2467 2468 (void) remove_reference(hdr, hash_lock, tag); 2469 if (hdr->b_l1hdr.b_datacnt > 1) { 2470 if (no_callback) 2471 arc_buf_destroy(buf, TRUE); 2472 } else if (no_callback) { 2473 ASSERT(hdr->b_l1hdr.b_buf == buf && buf->b_next == NULL); 2474 ASSERT(buf->b_efunc == NULL); 2475 hdr->b_flags |= ARC_FLAG_BUF_AVAILABLE; 2476 } 2477 ASSERT(no_callback || hdr->b_l1hdr.b_datacnt > 1 || 2478 refcount_is_zero(&hdr->b_l1hdr.b_refcnt)); 2479 mutex_exit(hash_lock); 2480 return (no_callback); 2481} 2482 2483int32_t 2484arc_buf_size(arc_buf_t *buf) 2485{ 2486 return (buf->b_hdr->b_size); 2487} 2488 2489/* 2490 * Called from the DMU to determine if the current buffer should be 2491 * evicted. In order to ensure proper locking, the eviction must be initiated 2492 * from the DMU. Return true if the buffer is associated with user data and 2493 * duplicate buffers still exist. 2494 */ 2495boolean_t 2496arc_buf_eviction_needed(arc_buf_t *buf) 2497{ 2498 arc_buf_hdr_t *hdr; 2499 boolean_t evict_needed = B_FALSE; 2500 2501 if (zfs_disable_dup_eviction) 2502 return (B_FALSE); 2503 2504 mutex_enter(&buf->b_evict_lock); 2505 hdr = buf->b_hdr; 2506 if (hdr == NULL) { 2507 /* 2508 * We are in arc_do_user_evicts(); let that function 2509 * perform the eviction. 2510 */ 2511 ASSERT(buf->b_data == NULL); 2512 mutex_exit(&buf->b_evict_lock); 2513 return (B_FALSE); 2514 } else if (buf->b_data == NULL) { 2515 /* 2516 * We have already been added to the arc eviction list; 2517 * recommend eviction. 2518 */ 2519 ASSERT3P(hdr, ==, &arc_eviction_hdr); 2520 mutex_exit(&buf->b_evict_lock); 2521 return (B_TRUE); 2522 } 2523 2524 if (hdr->b_l1hdr.b_datacnt > 1 && HDR_ISTYPE_DATA(hdr)) 2525 evict_needed = B_TRUE; 2526 2527 mutex_exit(&buf->b_evict_lock); 2528 return (evict_needed); 2529} 2530 2531/* 2532 * Evict the arc_buf_hdr that is provided as a parameter. The resultant 2533 * state of the header is dependent on it's state prior to entering this 2534 * function. The following transitions are possible: 2535 * 2536 * - arc_mru -> arc_mru_ghost 2537 * - arc_mfu -> arc_mfu_ghost 2538 * - arc_mru_ghost -> arc_l2c_only 2539 * - arc_mru_ghost -> deleted 2540 * - arc_mfu_ghost -> arc_l2c_only 2541 * - arc_mfu_ghost -> deleted 2542 */ 2543static int64_t 2544arc_evict_hdr(arc_buf_hdr_t *hdr, kmutex_t *hash_lock) 2545{ 2546 arc_state_t *evicted_state, *state; 2547 int64_t bytes_evicted = 0; 2548 2549 ASSERT(MUTEX_HELD(hash_lock)); 2550 ASSERT(HDR_HAS_L1HDR(hdr)); 2551 2552 state = hdr->b_l1hdr.b_state; 2553 if (GHOST_STATE(state)) { 2554 ASSERT(!HDR_IO_IN_PROGRESS(hdr)); 2555 ASSERT(hdr->b_l1hdr.b_buf == NULL); 2556 2557 /* 2558 * l2arc_write_buffers() relies on a header's L1 portion 2559 * (i.e. it's b_tmp_cdata field) during it's write phase. 2560 * Thus, we cannot push a header onto the arc_l2c_only 2561 * state (removing it's L1 piece) until the header is 2562 * done being written to the l2arc. 2563 */ 2564 if (HDR_HAS_L2HDR(hdr) && HDR_L2_WRITING(hdr)) { 2565 ARCSTAT_BUMP(arcstat_evict_l2_skip); 2566 return (bytes_evicted); 2567 } 2568 2569 ARCSTAT_BUMP(arcstat_deleted); 2570 bytes_evicted += hdr->b_size; 2571 2572 DTRACE_PROBE1(arc__delete, arc_buf_hdr_t *, hdr); 2573 2574 if (HDR_HAS_L2HDR(hdr)) { 2575 /* 2576 * This buffer is cached on the 2nd Level ARC; 2577 * don't destroy the header. 2578 */ 2579 arc_change_state(arc_l2c_only, hdr, hash_lock); 2580 /* 2581 * dropping from L1+L2 cached to L2-only, 2582 * realloc to remove the L1 header. 2583 */ 2584 hdr = arc_hdr_realloc(hdr, hdr_full_cache, 2585 hdr_l2only_cache); 2586 } else { 2587 arc_change_state(arc_anon, hdr, hash_lock); 2588 arc_hdr_destroy(hdr); 2589 } 2590 return (bytes_evicted); 2591 } 2592 2593 ASSERT(state == arc_mru || state == arc_mfu); 2594 evicted_state = (state == arc_mru) ? arc_mru_ghost : arc_mfu_ghost; 2595 2596 /* prefetch buffers have a minimum lifespan */ 2597 if (HDR_IO_IN_PROGRESS(hdr) || 2598 ((hdr->b_flags & (ARC_FLAG_PREFETCH | ARC_FLAG_INDIRECT)) && 2599 ddi_get_lbolt() - hdr->b_l1hdr.b_arc_access < 2600 arc_min_prefetch_lifespan)) { 2601 ARCSTAT_BUMP(arcstat_evict_skip); 2602 return (bytes_evicted); 2603 } 2604 2605 ASSERT0(refcount_count(&hdr->b_l1hdr.b_refcnt)); 2606 ASSERT3U(hdr->b_l1hdr.b_datacnt, >, 0); 2607 while (hdr->b_l1hdr.b_buf) { 2608 arc_buf_t *buf = hdr->b_l1hdr.b_buf; 2609 if (!mutex_tryenter(&buf->b_evict_lock)) { 2610 ARCSTAT_BUMP(arcstat_mutex_miss); 2611 break; 2612 } 2613 if (buf->b_data != NULL) 2614 bytes_evicted += hdr->b_size; 2615 if (buf->b_efunc != NULL) { 2616 mutex_enter(&arc_user_evicts_lock); 2617 arc_buf_destroy(buf, FALSE); 2618 hdr->b_l1hdr.b_buf = buf->b_next; 2619 buf->b_hdr = &arc_eviction_hdr; 2620 buf->b_next = arc_eviction_list; 2621 arc_eviction_list = buf; 2622 cv_signal(&arc_user_evicts_cv); 2623 mutex_exit(&arc_user_evicts_lock); 2624 mutex_exit(&buf->b_evict_lock); 2625 } else { 2626 mutex_exit(&buf->b_evict_lock); 2627 arc_buf_destroy(buf, TRUE); 2628 } 2629 } 2630 2631 if (HDR_HAS_L2HDR(hdr)) { 2632 ARCSTAT_INCR(arcstat_evict_l2_cached, hdr->b_size); 2633 } else { 2634 if (l2arc_write_eligible(hdr->b_spa, hdr)) 2635 ARCSTAT_INCR(arcstat_evict_l2_eligible, hdr->b_size); 2636 else 2637 ARCSTAT_INCR(arcstat_evict_l2_ineligible, hdr->b_size); 2638 } 2639 2640 if (hdr->b_l1hdr.b_datacnt == 0) { 2641 arc_change_state(evicted_state, hdr, hash_lock); 2642 ASSERT(HDR_IN_HASH_TABLE(hdr)); 2643 hdr->b_flags |= ARC_FLAG_IN_HASH_TABLE; 2644 hdr->b_flags &= ~ARC_FLAG_BUF_AVAILABLE; 2645 DTRACE_PROBE1(arc__evict, arc_buf_hdr_t *, hdr); 2646 } 2647 2648 return (bytes_evicted); 2649} 2650 2651static uint64_t 2652arc_evict_state_impl(multilist_t *ml, int idx, arc_buf_hdr_t *marker, 2653 uint64_t spa, int64_t bytes) 2654{ 2655 multilist_sublist_t *mls; 2656 uint64_t bytes_evicted = 0; 2657 arc_buf_hdr_t *hdr; 2658 kmutex_t *hash_lock; 2659 int evict_count = 0; 2660 2661 ASSERT3P(marker, !=, NULL); 2662 IMPLY(bytes < 0, bytes == ARC_EVICT_ALL); 2663 2664 mls = multilist_sublist_lock(ml, idx); 2665 2666 for (hdr = multilist_sublist_prev(mls, marker); hdr != NULL; 2667 hdr = multilist_sublist_prev(mls, marker)) { 2668 if ((bytes != ARC_EVICT_ALL && bytes_evicted >= bytes) || 2669 (evict_count >= zfs_arc_evict_batch_limit)) 2670 break; 2671 2672 /* 2673 * To keep our iteration location, move the marker 2674 * forward. Since we're not holding hdr's hash lock, we 2675 * must be very careful and not remove 'hdr' from the 2676 * sublist. Otherwise, other consumers might mistake the 2677 * 'hdr' as not being on a sublist when they call the 2678 * multilist_link_active() function (they all rely on 2679 * the hash lock protecting concurrent insertions and 2680 * removals). multilist_sublist_move_forward() was 2681 * specifically implemented to ensure this is the case 2682 * (only 'marker' will be removed and re-inserted). 2683 */ 2684 multilist_sublist_move_forward(mls, marker); 2685 2686 /* 2687 * The only case where the b_spa field should ever be 2688 * zero, is the marker headers inserted by 2689 * arc_evict_state(). It's possible for multiple threads 2690 * to be calling arc_evict_state() concurrently (e.g. 2691 * dsl_pool_close() and zio_inject_fault()), so we must 2692 * skip any markers we see from these other threads. 2693 */ 2694 if (hdr->b_spa == 0) 2695 continue; 2696 2697 /* we're only interested in evicting buffers of a certain spa */ 2698 if (spa != 0 && hdr->b_spa != spa) { 2699 ARCSTAT_BUMP(arcstat_evict_skip); 2700 continue; 2701 } 2702 2703 hash_lock = HDR_LOCK(hdr); 2704 2705 /* 2706 * We aren't calling this function from any code path 2707 * that would already be holding a hash lock, so we're 2708 * asserting on this assumption to be defensive in case 2709 * this ever changes. Without this check, it would be 2710 * possible to incorrectly increment arcstat_mutex_miss 2711 * below (e.g. if the code changed such that we called 2712 * this function with a hash lock held). 2713 */ 2714 ASSERT(!MUTEX_HELD(hash_lock)); 2715 2716 if (mutex_tryenter(hash_lock)) { 2717 uint64_t evicted = arc_evict_hdr(hdr, hash_lock); 2718 mutex_exit(hash_lock); 2719 2720 bytes_evicted += evicted; 2721 2722 /* 2723 * If evicted is zero, arc_evict_hdr() must have 2724 * decided to skip this header, don't increment 2725 * evict_count in this case. 2726 */ 2727 if (evicted != 0) 2728 evict_count++; 2729 2730 /* 2731 * If arc_size isn't overflowing, signal any 2732 * threads that might happen to be waiting. 2733 * 2734 * For each header evicted, we wake up a single 2735 * thread. If we used cv_broadcast, we could 2736 * wake up "too many" threads causing arc_size 2737 * to significantly overflow arc_c; since 2738 * arc_get_data_buf() doesn't check for overflow 2739 * when it's woken up (it doesn't because it's 2740 * possible for the ARC to be overflowing while 2741 * full of un-evictable buffers, and the 2742 * function should proceed in this case). 2743 * 2744 * If threads are left sleeping, due to not 2745 * using cv_broadcast, they will be woken up 2746 * just before arc_reclaim_thread() sleeps. 2747 */ 2748 mutex_enter(&arc_reclaim_lock); 2749 if (!arc_is_overflowing()) 2750 cv_signal(&arc_reclaim_waiters_cv); 2751 mutex_exit(&arc_reclaim_lock); 2752 } else { 2753 ARCSTAT_BUMP(arcstat_mutex_miss); 2754 } 2755 } 2756 2757 multilist_sublist_unlock(mls); 2758 2759 return (bytes_evicted); 2760} 2761 2762/* 2763 * Evict buffers from the given arc state, until we've removed the 2764 * specified number of bytes. Move the removed buffers to the 2765 * appropriate evict state. 2766 * 2767 * This function makes a "best effort". It skips over any buffers 2768 * it can't get a hash_lock on, and so, may not catch all candidates. 2769 * It may also return without evicting as much space as requested. 2770 * 2771 * If bytes is specified using the special value ARC_EVICT_ALL, this 2772 * will evict all available (i.e. unlocked and evictable) buffers from 2773 * the given arc state; which is used by arc_flush(). 2774 */ 2775static uint64_t 2776arc_evict_state(arc_state_t *state, uint64_t spa, int64_t bytes, 2777 arc_buf_contents_t type) 2778{ 2779 uint64_t total_evicted = 0; 2780 multilist_t *ml = &state->arcs_list[type]; 2781 int num_sublists; 2782 arc_buf_hdr_t **markers; 2783 2784 IMPLY(bytes < 0, bytes == ARC_EVICT_ALL); 2785 2786 num_sublists = multilist_get_num_sublists(ml); 2787 2788 /* 2789 * If we've tried to evict from each sublist, made some 2790 * progress, but still have not hit the target number of bytes 2791 * to evict, we want to keep trying. The markers allow us to 2792 * pick up where we left off for each individual sublist, rather 2793 * than starting from the tail each time. 2794 */ 2795 markers = kmem_zalloc(sizeof (*markers) * num_sublists, KM_SLEEP); 2796 for (int i = 0; i < num_sublists; i++) { 2797 markers[i] = kmem_cache_alloc(hdr_full_cache, KM_SLEEP); 2798 2799 /* 2800 * A b_spa of 0 is used to indicate that this header is 2801 * a marker. This fact is used in arc_adjust_type() and 2802 * arc_evict_state_impl(). 2803 */ 2804 markers[i]->b_spa = 0; 2805 2806 multilist_sublist_t *mls = multilist_sublist_lock(ml, i); 2807 multilist_sublist_insert_tail(mls, markers[i]); 2808 multilist_sublist_unlock(mls); 2809 } 2810 2811 /* 2812 * While we haven't hit our target number of bytes to evict, or 2813 * we're evicting all available buffers. 2814 */ 2815 while (total_evicted < bytes || bytes == ARC_EVICT_ALL) { 2816 /* 2817 * Start eviction using a randomly selected sublist, 2818 * this is to try and evenly balance eviction across all 2819 * sublists. Always starting at the same sublist 2820 * (e.g. index 0) would cause evictions to favor certain 2821 * sublists over others. 2822 */ 2823 int sublist_idx = multilist_get_random_index(ml); 2824 uint64_t scan_evicted = 0; 2825 2826 for (int i = 0; i < num_sublists; i++) { 2827 uint64_t bytes_remaining; 2828 uint64_t bytes_evicted; 2829 2830 if (bytes == ARC_EVICT_ALL) 2831 bytes_remaining = ARC_EVICT_ALL; 2832 else if (total_evicted < bytes) 2833 bytes_remaining = bytes - total_evicted; 2834 else 2835 break; 2836 2837 bytes_evicted = arc_evict_state_impl(ml, sublist_idx, 2838 markers[sublist_idx], spa, bytes_remaining); 2839 2840 scan_evicted += bytes_evicted; 2841 total_evicted += bytes_evicted; 2842 2843 /* we've reached the end, wrap to the beginning */ 2844 if (++sublist_idx >= num_sublists) 2845 sublist_idx = 0; 2846 } 2847 2848 /* 2849 * If we didn't evict anything during this scan, we have 2850 * no reason to believe we'll evict more during another 2851 * scan, so break the loop. 2852 */ 2853 if (scan_evicted == 0) { 2854 /* This isn't possible, let's make that obvious */ 2855 ASSERT3S(bytes, !=, 0); 2856 2857 /* 2858 * When bytes is ARC_EVICT_ALL, the only way to 2859 * break the loop is when scan_evicted is zero. 2860 * In that case, we actually have evicted enough, 2861 * so we don't want to increment the kstat. 2862 */ 2863 if (bytes != ARC_EVICT_ALL) { 2864 ASSERT3S(total_evicted, <, bytes); 2865 ARCSTAT_BUMP(arcstat_evict_not_enough); 2866 } 2867 2868 break; 2869 } 2870 } 2871 2872 for (int i = 0; i < num_sublists; i++) { 2873 multilist_sublist_t *mls = multilist_sublist_lock(ml, i); 2874 multilist_sublist_remove(mls, markers[i]); 2875 multilist_sublist_unlock(mls); 2876 2877 kmem_cache_free(hdr_full_cache, markers[i]); 2878 } 2879 kmem_free(markers, sizeof (*markers) * num_sublists); 2880 2881 return (total_evicted); 2882} 2883 2884/* 2885 * Flush all "evictable" data of the given type from the arc state 2886 * specified. This will not evict any "active" buffers (i.e. referenced). 2887 * 2888 * When 'retry' is set to FALSE, the function will make a single pass 2889 * over the state and evict any buffers that it can. Since it doesn't 2890 * continually retry the eviction, it might end up leaving some buffers 2891 * in the ARC due to lock misses. 2892 * 2893 * When 'retry' is set to TRUE, the function will continually retry the 2894 * eviction until *all* evictable buffers have been removed from the 2895 * state. As a result, if concurrent insertions into the state are 2896 * allowed (e.g. if the ARC isn't shutting down), this function might 2897 * wind up in an infinite loop, continually trying to evict buffers. 2898 */ 2899static uint64_t 2900arc_flush_state(arc_state_t *state, uint64_t spa, arc_buf_contents_t type, 2901 boolean_t retry) 2902{ 2903 uint64_t evicted = 0; 2904 2905 while (state->arcs_lsize[type] != 0) { 2906 evicted += arc_evict_state(state, spa, ARC_EVICT_ALL, type); 2907 2908 if (!retry) 2909 break; 2910 } 2911 2912 return (evicted); 2913} 2914 2915/* 2916 * Evict the specified number of bytes from the state specified, 2917 * restricting eviction to the spa and type given. This function 2918 * prevents us from trying to evict more from a state's list than 2919 * is "evictable", and to skip evicting altogether when passed a 2920 * negative value for "bytes". In contrast, arc_evict_state() will 2921 * evict everything it can, when passed a negative value for "bytes". 2922 */ 2923static uint64_t 2924arc_adjust_impl(arc_state_t *state, uint64_t spa, int64_t bytes, 2925 arc_buf_contents_t type) 2926{ 2927 int64_t delta; 2928 2929 if (bytes > 0 && state->arcs_lsize[type] > 0) { 2930 delta = MIN(state->arcs_lsize[type], bytes); 2931 return (arc_evict_state(state, spa, delta, type)); 2932 } 2933 2934 return (0); 2935} 2936 2937/* 2938 * Evict metadata buffers from the cache, such that arc_meta_used is 2939 * capped by the arc_meta_limit tunable. 2940 */ 2941static uint64_t 2942arc_adjust_meta(void) 2943{ 2944 uint64_t total_evicted = 0; 2945 int64_t target; 2946 2947 /* 2948 * If we're over the meta limit, we want to evict enough 2949 * metadata to get back under the meta limit. We don't want to 2950 * evict so much that we drop the MRU below arc_p, though. If 2951 * we're over the meta limit more than we're over arc_p, we 2952 * evict some from the MRU here, and some from the MFU below. 2953 */ 2954 target = MIN((int64_t)(arc_meta_used - arc_meta_limit), 2955 (int64_t)(arc_anon->arcs_size + arc_mru->arcs_size - arc_p)); 2956 2957 total_evicted += arc_adjust_impl(arc_mru, 0, target, ARC_BUFC_METADATA); 2958 2959 /* 2960 * Similar to the above, we want to evict enough bytes to get us 2961 * below the meta limit, but not so much as to drop us below the 2962 * space alloted to the MFU (which is defined as arc_c - arc_p). 2963 */ 2964 target = MIN((int64_t)(arc_meta_used - arc_meta_limit), 2965 (int64_t)(arc_mfu->arcs_size - (arc_c - arc_p))); 2966 2967 total_evicted += arc_adjust_impl(arc_mfu, 0, target, ARC_BUFC_METADATA); 2968 2969 return (total_evicted); 2970} 2971 2972/* 2973 * Return the type of the oldest buffer in the given arc state 2974 * 2975 * This function will select a random sublist of type ARC_BUFC_DATA and 2976 * a random sublist of type ARC_BUFC_METADATA. The tail of each sublist 2977 * is compared, and the type which contains the "older" buffer will be 2978 * returned. 2979 */ 2980static arc_buf_contents_t 2981arc_adjust_type(arc_state_t *state) 2982{ 2983 multilist_t *data_ml = &state->arcs_list[ARC_BUFC_DATA]; 2984 multilist_t *meta_ml = &state->arcs_list[ARC_BUFC_METADATA]; 2985 int data_idx = multilist_get_random_index(data_ml); 2986 int meta_idx = multilist_get_random_index(meta_ml); 2987 multilist_sublist_t *data_mls; 2988 multilist_sublist_t *meta_mls; 2989 arc_buf_contents_t type; 2990 arc_buf_hdr_t *data_hdr; 2991 arc_buf_hdr_t *meta_hdr; 2992 2993 /* 2994 * We keep the sublist lock until we're finished, to prevent 2995 * the headers from being destroyed via arc_evict_state(). 2996 */ 2997 data_mls = multilist_sublist_lock(data_ml, data_idx); 2998 meta_mls = multilist_sublist_lock(meta_ml, meta_idx); 2999 3000 /* 3001 * These two loops are to ensure we skip any markers that 3002 * might be at the tail of the lists due to arc_evict_state(). 3003 */ 3004 3005 for (data_hdr = multilist_sublist_tail(data_mls); data_hdr != NULL; 3006 data_hdr = multilist_sublist_prev(data_mls, data_hdr)) { 3007 if (data_hdr->b_spa != 0) 3008 break; 3009 } 3010 3011 for (meta_hdr = multilist_sublist_tail(meta_mls); meta_hdr != NULL; 3012 meta_hdr = multilist_sublist_prev(meta_mls, meta_hdr)) { 3013 if (meta_hdr->b_spa != 0) 3014 break; 3015 } 3016 3017 if (data_hdr == NULL && meta_hdr == NULL) { 3018 type = ARC_BUFC_DATA; 3019 } else if (data_hdr == NULL) { 3020 ASSERT3P(meta_hdr, !=, NULL); 3021 type = ARC_BUFC_METADATA; 3022 } else if (meta_hdr == NULL) { 3023 ASSERT3P(data_hdr, !=, NULL); 3024 type = ARC_BUFC_DATA; 3025 } else { 3026 ASSERT3P(data_hdr, !=, NULL); 3027 ASSERT3P(meta_hdr, !=, NULL); 3028 3029 /* The headers can't be on the sublist without an L1 header */ 3030 ASSERT(HDR_HAS_L1HDR(data_hdr)); 3031 ASSERT(HDR_HAS_L1HDR(meta_hdr)); 3032 3033 if (data_hdr->b_l1hdr.b_arc_access < 3034 meta_hdr->b_l1hdr.b_arc_access) { 3035 type = ARC_BUFC_DATA; 3036 } else { 3037 type = ARC_BUFC_METADATA; 3038 } 3039 } 3040 3041 multilist_sublist_unlock(meta_mls); 3042 multilist_sublist_unlock(data_mls); 3043 3044 return (type); 3045} 3046 3047/* 3048 * Evict buffers from the cache, such that arc_size is capped by arc_c. 3049 */ 3050static uint64_t 3051arc_adjust(void) 3052{ 3053 uint64_t total_evicted = 0; 3054 uint64_t bytes; 3055 int64_t target; 3056 3057 /* 3058 * If we're over arc_meta_limit, we want to correct that before 3059 * potentially evicting data buffers below. 3060 */ 3061 total_evicted += arc_adjust_meta(); 3062 3063 /* 3064 * Adjust MRU size 3065 * 3066 * If we're over the target cache size, we want to evict enough 3067 * from the list to get back to our target size. We don't want 3068 * to evict too much from the MRU, such that it drops below 3069 * arc_p. So, if we're over our target cache size more than 3070 * the MRU is over arc_p, we'll evict enough to get back to 3071 * arc_p here, and then evict more from the MFU below. 3072 */ 3073 target = MIN((int64_t)(arc_size - arc_c), 3074 (int64_t)(arc_anon->arcs_size + arc_mru->arcs_size + arc_meta_used - 3075 arc_p)); 3076 3077 /* 3078 * If we're below arc_meta_min, always prefer to evict data. 3079 * Otherwise, try to satisfy the requested number of bytes to 3080 * evict from the type which contains older buffers; in an 3081 * effort to keep newer buffers in the cache regardless of their 3082 * type. If we cannot satisfy the number of bytes from this 3083 * type, spill over into the next type. 3084 */ 3085 if (arc_adjust_type(arc_mru) == ARC_BUFC_METADATA && 3086 arc_meta_used > arc_meta_min) { 3087 bytes = arc_adjust_impl(arc_mru, 0, target, ARC_BUFC_METADATA); 3088 total_evicted += bytes; 3089 3090 /* 3091 * If we couldn't evict our target number of bytes from 3092 * metadata, we try to get the rest from data. 3093 */ 3094 target -= bytes; 3095 3096 total_evicted += 3097 arc_adjust_impl(arc_mru, 0, target, ARC_BUFC_DATA); 3098 } else { 3099 bytes = arc_adjust_impl(arc_mru, 0, target, ARC_BUFC_DATA); 3100 total_evicted += bytes; 3101 3102 /* 3103 * If we couldn't evict our target number of bytes from 3104 * data, we try to get the rest from metadata. 3105 */ 3106 target -= bytes; 3107 3108 total_evicted += 3109 arc_adjust_impl(arc_mru, 0, target, ARC_BUFC_METADATA); 3110 } 3111 3112 /* 3113 * Adjust MFU size 3114 * 3115 * Now that we've tried to evict enough from the MRU to get its 3116 * size back to arc_p, if we're still above the target cache 3117 * size, we evict the rest from the MFU. 3118 */ 3119 target = arc_size - arc_c; 3120 3121 if (arc_adjust_type(arc_mru) == ARC_BUFC_METADATA && 3122 arc_meta_used > arc_meta_min) { 3123 bytes = arc_adjust_impl(arc_mfu, 0, target, ARC_BUFC_METADATA); 3124 total_evicted += bytes; 3125 3126 /* 3127 * If we couldn't evict our target number of bytes from 3128 * metadata, we try to get the rest from data. 3129 */ 3130 target -= bytes; 3131 3132 total_evicted += 3133 arc_adjust_impl(arc_mfu, 0, target, ARC_BUFC_DATA); 3134 } else { 3135 bytes = arc_adjust_impl(arc_mfu, 0, target, ARC_BUFC_DATA); 3136 total_evicted += bytes; 3137 3138 /* 3139 * If we couldn't evict our target number of bytes from 3140 * data, we try to get the rest from data. 3141 */ 3142 target -= bytes; 3143 3144 total_evicted += 3145 arc_adjust_impl(arc_mfu, 0, target, ARC_BUFC_METADATA); 3146 } 3147 3148 /* 3149 * Adjust ghost lists 3150 * 3151 * In addition to the above, the ARC also defines target values 3152 * for the ghost lists. The sum of the mru list and mru ghost 3153 * list should never exceed the target size of the cache, and 3154 * the sum of the mru list, mfu list, mru ghost list, and mfu 3155 * ghost list should never exceed twice the target size of the 3156 * cache. The following logic enforces these limits on the ghost 3157 * caches, and evicts from them as needed. 3158 */ 3159 target = arc_mru->arcs_size + arc_mru_ghost->arcs_size - arc_c; 3160 3161 bytes = arc_adjust_impl(arc_mru_ghost, 0, target, ARC_BUFC_DATA); 3162 total_evicted += bytes; 3163 3164 target -= bytes; 3165 3166 total_evicted += 3167 arc_adjust_impl(arc_mru_ghost, 0, target, ARC_BUFC_METADATA); 3168 3169 /* 3170 * We assume the sum of the mru list and mfu list is less than 3171 * or equal to arc_c (we enforced this above), which means we 3172 * can use the simpler of the two equations below: 3173 * 3174 * mru + mfu + mru ghost + mfu ghost <= 2 * arc_c 3175 * mru ghost + mfu ghost <= arc_c 3176 */ 3177 target = arc_mru_ghost->arcs_size + arc_mfu_ghost->arcs_size - arc_c; 3178 3179 bytes = arc_adjust_impl(arc_mfu_ghost, 0, target, ARC_BUFC_DATA); 3180 total_evicted += bytes; 3181 3182 target -= bytes; 3183 3184 total_evicted += 3185 arc_adjust_impl(arc_mfu_ghost, 0, target, ARC_BUFC_METADATA); 3186 3187 return (total_evicted); 3188} 3189 3190static void 3191arc_do_user_evicts(void) 3192{ 3193 mutex_enter(&arc_user_evicts_lock); 3194 while (arc_eviction_list != NULL) { 3195 arc_buf_t *buf = arc_eviction_list; 3196 arc_eviction_list = buf->b_next; 3197 mutex_enter(&buf->b_evict_lock); 3198 buf->b_hdr = NULL; 3199 mutex_exit(&buf->b_evict_lock); 3200 mutex_exit(&arc_user_evicts_lock); 3201 3202 if (buf->b_efunc != NULL) 3203 VERIFY0(buf->b_efunc(buf->b_private)); 3204 3205 buf->b_efunc = NULL; 3206 buf->b_private = NULL; 3207 kmem_cache_free(buf_cache, buf); 3208 mutex_enter(&arc_user_evicts_lock); 3209 } 3210 mutex_exit(&arc_user_evicts_lock); 3211} 3212 3213void 3214arc_flush(spa_t *spa, boolean_t retry) 3215{ 3216 uint64_t guid = 0; 3217 3218 /* 3219 * If retry is TRUE, a spa must not be specified since we have 3220 * no good way to determine if all of a spa's buffers have been 3221 * evicted from an arc state. 3222 */ 3223 ASSERT(!retry || spa == 0); 3224 3225 if (spa != NULL) 3226 guid = spa_load_guid(spa); 3227 3228 (void) arc_flush_state(arc_mru, guid, ARC_BUFC_DATA, retry); 3229 (void) arc_flush_state(arc_mru, guid, ARC_BUFC_METADATA, retry); 3230 3231 (void) arc_flush_state(arc_mfu, guid, ARC_BUFC_DATA, retry); 3232 (void) arc_flush_state(arc_mfu, guid, ARC_BUFC_METADATA, retry); 3233 3234 (void) arc_flush_state(arc_mru_ghost, guid, ARC_BUFC_DATA, retry); 3235 (void) arc_flush_state(arc_mru_ghost, guid, ARC_BUFC_METADATA, retry); 3236 3237 (void) arc_flush_state(arc_mfu_ghost, guid, ARC_BUFC_DATA, retry); 3238 (void) arc_flush_state(arc_mfu_ghost, guid, ARC_BUFC_METADATA, retry); 3239 3240 arc_do_user_evicts(); 3241 ASSERT(spa || arc_eviction_list == NULL); 3242} 3243 3244void 3245arc_shrink(int64_t to_free) 3246{ 3247 if (arc_c > arc_c_min) { 3248 DTRACE_PROBE4(arc__shrink, uint64_t, arc_c, uint64_t, 3249 arc_c_min, uint64_t, arc_p, uint64_t, to_free); 3250 if (arc_c > arc_c_min + to_free) 3251 atomic_add_64(&arc_c, -to_free); 3252 else 3253 arc_c = arc_c_min; 3254 3255 atomic_add_64(&arc_p, -(arc_p >> arc_shrink_shift)); 3256 if (arc_c > arc_size) 3257 arc_c = MAX(arc_size, arc_c_min); 3258 if (arc_p > arc_c) 3259 arc_p = (arc_c >> 1); 3260 3261 DTRACE_PROBE2(arc__shrunk, uint64_t, arc_c, uint64_t, 3262 arc_p); 3263 3264 ASSERT(arc_c >= arc_c_min); 3265 ASSERT((int64_t)arc_p >= 0); 3266 } 3267 3268 if (arc_size > arc_c) { 3269 DTRACE_PROBE2(arc__shrink_adjust, uint64_t, arc_size, 3270 uint64_t, arc_c); 3271 (void) arc_adjust(); 3272 } 3273} 3274 3275static long needfree = 0; 3276 3277typedef enum free_memory_reason_t { 3278 FMR_UNKNOWN, 3279 FMR_NEEDFREE, 3280 FMR_LOTSFREE, 3281 FMR_SWAPFS_MINFREE, 3282 FMR_PAGES_PP_MAXIMUM, 3283 FMR_HEAP_ARENA, 3284 FMR_ZIO_ARENA, 3285 FMR_ZIO_FRAG, 3286} free_memory_reason_t; 3287 3288int64_t last_free_memory; 3289free_memory_reason_t last_free_reason; 3290 3291/* 3292 * Additional reserve of pages for pp_reserve. 3293 */ 3294int64_t arc_pages_pp_reserve = 64; 3295 3296/* 3297 * Additional reserve of pages for swapfs. 3298 */ 3299int64_t arc_swapfs_reserve = 64; 3300 3301/* 3302 * Return the amount of memory that can be consumed before reclaim will be 3303 * needed. Positive if there is sufficient free memory, negative indicates 3304 * the amount of memory that needs to be freed up. 3305 */ 3306static int64_t 3307arc_available_memory(void) 3308{ 3309 int64_t lowest = INT64_MAX; 3310 int64_t n; 3311 free_memory_reason_t r = FMR_UNKNOWN; 3312 3313#ifdef _KERNEL 3314 if (needfree > 0) { 3315 n = PAGESIZE * (-needfree); 3316 if (n < lowest) { 3317 lowest = n; 3318 r = FMR_NEEDFREE; 3319 } 3320 } 3321 3322 /* 3323 * Cooperate with pagedaemon when it's time for it to scan 3324 * and reclaim some pages. 3325 */ 3326 n = PAGESIZE * ((int64_t)freemem - zfs_arc_free_target); 3327 if (n < lowest) { 3328 lowest = n; 3329 r = FMR_LOTSFREE; 3330 } 3331 3332#ifdef sun 3333 /* 3334 * check that we're out of range of the pageout scanner. It starts to 3335 * schedule paging if freemem is less than lotsfree and needfree. 3336 * lotsfree is the high-water mark for pageout, and needfree is the 3337 * number of needed free pages. We add extra pages here to make sure 3338 * the scanner doesn't start up while we're freeing memory. 3339 */ 3340 n = PAGESIZE * (freemem - lotsfree - needfree - desfree); 3341 if (n < lowest) { 3342 lowest = n; 3343 r = FMR_LOTSFREE; 3344 } 3345 3346 /* 3347 * check to make sure that swapfs has enough space so that anon 3348 * reservations can still succeed. anon_resvmem() checks that the 3349 * availrmem is greater than swapfs_minfree, and the number of reserved 3350 * swap pages. We also add a bit of extra here just to prevent 3351 * circumstances from getting really dire. 3352 */ 3353 n = PAGESIZE * (availrmem - swapfs_minfree - swapfs_reserve - 3354 desfree - arc_swapfs_reserve); 3355 if (n < lowest) { 3356 lowest = n; 3357 r = FMR_SWAPFS_MINFREE; 3358 } 3359 3360 3361 /* 3362 * Check that we have enough availrmem that memory locking (e.g., via 3363 * mlock(3C) or memcntl(2)) can still succeed. (pages_pp_maximum 3364 * stores the number of pages that cannot be locked; when availrmem 3365 * drops below pages_pp_maximum, page locking mechanisms such as 3366 * page_pp_lock() will fail.) 3367 */ 3368 n = PAGESIZE * (availrmem - pages_pp_maximum - 3369 arc_pages_pp_reserve); 3370 if (n < lowest) { 3371 lowest = n; 3372 r = FMR_PAGES_PP_MAXIMUM; 3373 } 3374 3375#endif /* sun */ 3376#if defined(__i386) || !defined(UMA_MD_SMALL_ALLOC) 3377 /* 3378 * If we're on an i386 platform, it's possible that we'll exhaust the 3379 * kernel heap space before we ever run out of available physical 3380 * memory. Most checks of the size of the heap_area compare against 3381 * tune.t_minarmem, which is the minimum available real memory that we 3382 * can have in the system. However, this is generally fixed at 25 pages 3383 * which is so low that it's useless. In this comparison, we seek to 3384 * calculate the total heap-size, and reclaim if more than 3/4ths of the 3385 * heap is allocated. (Or, in the calculation, if less than 1/4th is 3386 * free) 3387 */ 3388 n = (int64_t)vmem_size(heap_arena, VMEM_FREE) - 3389 (vmem_size(heap_arena, VMEM_FREE | VMEM_ALLOC) >> 2); 3390 if (n < lowest) { 3391 lowest = n; 3392 r = FMR_HEAP_ARENA; 3393 } 3394#define zio_arena NULL 3395#else 3396#define zio_arena heap_arena 3397#endif 3398 3399 /* 3400 * If zio data pages are being allocated out of a separate heap segment, 3401 * then enforce that the size of available vmem for this arena remains 3402 * above about 1/16th free. 3403 * 3404 * Note: The 1/16th arena free requirement was put in place 3405 * to aggressively evict memory from the arc in order to avoid 3406 * memory fragmentation issues. 3407 */ 3408 if (zio_arena != NULL) { 3409 n = (int64_t)vmem_size(zio_arena, VMEM_FREE) - 3410 (vmem_size(zio_arena, VMEM_ALLOC) >> 4); 3411 if (n < lowest) { 3412 lowest = n; 3413 r = FMR_ZIO_ARENA; 3414 } 3415 } 3416 3417 /* 3418 * Above limits know nothing about real level of KVA fragmentation. 3419 * Start aggressive reclamation if too little sequential KVA left. 3420 */ 3421 if (lowest > 0) { 3422 n = (vmem_size(heap_arena, VMEM_MAXFREE) < zfs_max_recordsize) ? 3423 -((int64_t)vmem_size(heap_arena, VMEM_ALLOC) >> 4) : 3424 INT64_MAX; 3425 if (n < lowest) { 3426 lowest = n; 3427 r = FMR_ZIO_FRAG; 3428 } 3429 } 3430 3431#else /* _KERNEL */ 3432 /* Every 100 calls, free a small amount */ 3433 if (spa_get_random(100) == 0) 3434 lowest = -1024; 3435#endif /* _KERNEL */ 3436 3437 last_free_memory = lowest; 3438 last_free_reason = r; 3439 DTRACE_PROBE2(arc__available_memory, int64_t, lowest, int, r); 3440 return (lowest); 3441} 3442 3443 3444/* 3445 * Determine if the system is under memory pressure and is asking 3446 * to reclaim memory. A return value of TRUE indicates that the system 3447 * is under memory pressure and that the arc should adjust accordingly. 3448 */ 3449static boolean_t 3450arc_reclaim_needed(void) 3451{ 3452 return (arc_available_memory() < 0); 3453} 3454 3455extern kmem_cache_t *zio_buf_cache[]; 3456extern kmem_cache_t *zio_data_buf_cache[]; 3457extern kmem_cache_t *range_seg_cache; 3458 3459static __noinline void 3460arc_kmem_reap_now(void) 3461{ 3462 size_t i; 3463 kmem_cache_t *prev_cache = NULL; 3464 kmem_cache_t *prev_data_cache = NULL; 3465 3466 DTRACE_PROBE(arc__kmem_reap_start); 3467#ifdef _KERNEL 3468 if (arc_meta_used >= arc_meta_limit) { 3469 /* 3470 * We are exceeding our meta-data cache limit. 3471 * Purge some DNLC entries to release holds on meta-data. 3472 */ 3473 dnlc_reduce_cache((void *)(uintptr_t)arc_reduce_dnlc_percent); 3474 } 3475#if defined(__i386) 3476 /* 3477 * Reclaim unused memory from all kmem caches. 3478 */ 3479 kmem_reap(); 3480#endif 3481#endif 3482 3483 for (i = 0; i < SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT; i++) { 3484 if (zio_buf_cache[i] != prev_cache) { 3485 prev_cache = zio_buf_cache[i]; 3486 kmem_cache_reap_now(zio_buf_cache[i]); 3487 } 3488 if (zio_data_buf_cache[i] != prev_data_cache) { 3489 prev_data_cache = zio_data_buf_cache[i]; 3490 kmem_cache_reap_now(zio_data_buf_cache[i]); 3491 } 3492 } 3493 kmem_cache_reap_now(buf_cache); 3494 kmem_cache_reap_now(hdr_full_cache); 3495 kmem_cache_reap_now(hdr_l2only_cache); 3496 kmem_cache_reap_now(range_seg_cache); 3497 3498#ifdef sun 3499 if (zio_arena != NULL) { 3500 /* 3501 * Ask the vmem arena to reclaim unused memory from its 3502 * quantum caches. 3503 */ 3504 vmem_qcache_reap(zio_arena); 3505 } 3506#endif 3507 DTRACE_PROBE(arc__kmem_reap_end); 3508} 3509 3510/* 3511 * Threads can block in arc_get_data_buf() waiting for this thread to evict 3512 * enough data and signal them to proceed. When this happens, the threads in 3513 * arc_get_data_buf() are sleeping while holding the hash lock for their 3514 * particular arc header. Thus, we must be careful to never sleep on a 3515 * hash lock in this thread. This is to prevent the following deadlock: 3516 * 3517 * - Thread A sleeps on CV in arc_get_data_buf() holding hash lock "L", 3518 * waiting for the reclaim thread to signal it. 3519 * 3520 * - arc_reclaim_thread() tries to acquire hash lock "L" using mutex_enter, 3521 * fails, and goes to sleep forever. 3522 * 3523 * This possible deadlock is avoided by always acquiring a hash lock 3524 * using mutex_tryenter() from arc_reclaim_thread(). 3525 */ 3526static void 3527arc_reclaim_thread(void *dummy __unused) 3528{ 3529 clock_t growtime = 0; 3530 callb_cpr_t cpr; 3531 3532 CALLB_CPR_INIT(&cpr, &arc_reclaim_lock, callb_generic_cpr, FTAG); 3533 3534 mutex_enter(&arc_reclaim_lock); 3535 while (!arc_reclaim_thread_exit) { 3536 int64_t free_memory = arc_available_memory(); 3537 uint64_t evicted = 0; 3538 3539 mutex_exit(&arc_reclaim_lock); 3540 3541 if (free_memory < 0) { 3542 3543 arc_no_grow = B_TRUE; 3544 arc_warm = B_TRUE; 3545 3546 /* 3547 * Wait at least zfs_grow_retry (default 60) seconds 3548 * before considering growing. 3549 */ 3550 growtime = ddi_get_lbolt() + (arc_grow_retry * hz); 3551 3552 arc_kmem_reap_now(); 3553 3554 /* 3555 * If we are still low on memory, shrink the ARC 3556 * so that we have arc_shrink_min free space. 3557 */ 3558 free_memory = arc_available_memory(); 3559 3560 int64_t to_free = 3561 (arc_c >> arc_shrink_shift) - free_memory; 3562 if (to_free > 0) { 3563#ifdef _KERNEL 3564 to_free = MAX(to_free, ptob(needfree)); 3565#endif 3566 arc_shrink(to_free); 3567 } 3568 } else if (free_memory < arc_c >> arc_no_grow_shift) { 3569 arc_no_grow = B_TRUE; 3570 } else if (ddi_get_lbolt() >= growtime) { 3571 arc_no_grow = B_FALSE; 3572 } 3573 3574 evicted = arc_adjust(); 3575 3576 mutex_enter(&arc_reclaim_lock); 3577 3578 /* 3579 * If evicted is zero, we couldn't evict anything via 3580 * arc_adjust(). This could be due to hash lock 3581 * collisions, but more likely due to the majority of 3582 * arc buffers being unevictable. Therefore, even if 3583 * arc_size is above arc_c, another pass is unlikely to 3584 * be helpful and could potentially cause us to enter an 3585 * infinite loop. 3586 */ 3587 if (arc_size <= arc_c || evicted == 0) { 3588#ifdef _KERNEL 3589 needfree = 0; 3590#endif 3591 /* 3592 * We're either no longer overflowing, or we 3593 * can't evict anything more, so we should wake 3594 * up any threads before we go to sleep. 3595 */ 3596 cv_broadcast(&arc_reclaim_waiters_cv); 3597 3598 /* 3599 * Block until signaled, or after one second (we 3600 * might need to perform arc_kmem_reap_now() 3601 * even if we aren't being signalled) 3602 */ 3603 CALLB_CPR_SAFE_BEGIN(&cpr); 3604 (void) cv_timedwait(&arc_reclaim_thread_cv, 3605 &arc_reclaim_lock, hz); 3606 CALLB_CPR_SAFE_END(&cpr, &arc_reclaim_lock); 3607 } 3608 } 3609 3610 arc_reclaim_thread_exit = FALSE; 3611 cv_broadcast(&arc_reclaim_thread_cv); 3612 CALLB_CPR_EXIT(&cpr); /* drops arc_reclaim_lock */ 3613 thread_exit(); 3614} 3615 3616static void 3617arc_user_evicts_thread(void *dummy __unused) 3618{ 3619 callb_cpr_t cpr; 3620 3621 CALLB_CPR_INIT(&cpr, &arc_user_evicts_lock, callb_generic_cpr, FTAG); 3622 3623 mutex_enter(&arc_user_evicts_lock); 3624 while (!arc_user_evicts_thread_exit) { 3625 mutex_exit(&arc_user_evicts_lock); 3626 3627 arc_do_user_evicts(); 3628 3629 /* 3630 * This is necessary in order for the mdb ::arc dcmd to 3631 * show up to date information. Since the ::arc command 3632 * does not call the kstat's update function, without 3633 * this call, the command may show stale stats for the 3634 * anon, mru, mru_ghost, mfu, and mfu_ghost lists. Even 3635 * with this change, the data might be up to 1 second 3636 * out of date; but that should suffice. The arc_state_t 3637 * structures can be queried directly if more accurate 3638 * information is needed. 3639 */ 3640 if (arc_ksp != NULL) 3641 arc_ksp->ks_update(arc_ksp, KSTAT_READ); 3642 3643 mutex_enter(&arc_user_evicts_lock); 3644 3645 /* 3646 * Block until signaled, or after one second (we need to 3647 * call the arc's kstat update function regularly). 3648 */ 3649 CALLB_CPR_SAFE_BEGIN(&cpr); 3650 (void) cv_timedwait(&arc_user_evicts_cv, 3651 &arc_user_evicts_lock, hz); 3652 CALLB_CPR_SAFE_END(&cpr, &arc_user_evicts_lock); 3653 } 3654 3655 arc_user_evicts_thread_exit = FALSE; 3656 cv_broadcast(&arc_user_evicts_cv); 3657 CALLB_CPR_EXIT(&cpr); /* drops arc_user_evicts_lock */ 3658 thread_exit(); 3659} 3660 3661/* 3662 * Adapt arc info given the number of bytes we are trying to add and 3663 * the state that we are comming from. This function is only called 3664 * when we are adding new content to the cache. 3665 */ 3666static void 3667arc_adapt(int bytes, arc_state_t *state) 3668{ 3669 int mult; 3670 uint64_t arc_p_min = (arc_c >> arc_p_min_shift); 3671 3672 if (state == arc_l2c_only) 3673 return; 3674 3675 ASSERT(bytes > 0); 3676 /* 3677 * Adapt the target size of the MRU list: 3678 * - if we just hit in the MRU ghost list, then increase 3679 * the target size of the MRU list. 3680 * - if we just hit in the MFU ghost list, then increase 3681 * the target size of the MFU list by decreasing the 3682 * target size of the MRU list. 3683 */ 3684 if (state == arc_mru_ghost) { 3685 mult = ((arc_mru_ghost->arcs_size >= arc_mfu_ghost->arcs_size) ? 3686 1 : (arc_mfu_ghost->arcs_size/arc_mru_ghost->arcs_size)); 3687 mult = MIN(mult, 10); /* avoid wild arc_p adjustment */ 3688 3689 arc_p = MIN(arc_c - arc_p_min, arc_p + bytes * mult); 3690 } else if (state == arc_mfu_ghost) { 3691 uint64_t delta; 3692 3693 mult = ((arc_mfu_ghost->arcs_size >= arc_mru_ghost->arcs_size) ? 3694 1 : (arc_mru_ghost->arcs_size/arc_mfu_ghost->arcs_size)); 3695 mult = MIN(mult, 10); 3696 3697 delta = MIN(bytes * mult, arc_p); 3698 arc_p = MAX(arc_p_min, arc_p - delta); 3699 } 3700 ASSERT((int64_t)arc_p >= 0); 3701 3702 if (arc_reclaim_needed()) { 3703 cv_signal(&arc_reclaim_thread_cv); 3704 return; 3705 } 3706 3707 if (arc_no_grow) 3708 return; 3709 3710 if (arc_c >= arc_c_max) 3711 return; 3712 3713 /* 3714 * If we're within (2 * maxblocksize) bytes of the target 3715 * cache size, increment the target cache size 3716 */ 3717 if (arc_size > arc_c - (2ULL << SPA_MAXBLOCKSHIFT)) { 3718 DTRACE_PROBE1(arc__inc_adapt, int, bytes); 3719 atomic_add_64(&arc_c, (int64_t)bytes); 3720 if (arc_c > arc_c_max) 3721 arc_c = arc_c_max; 3722 else if (state == arc_anon) 3723 atomic_add_64(&arc_p, (int64_t)bytes); 3724 if (arc_p > arc_c) 3725 arc_p = arc_c; 3726 } 3727 ASSERT((int64_t)arc_p >= 0); 3728} 3729 3730/* 3731 * Check if arc_size has grown past our upper threshold, determined by 3732 * zfs_arc_overflow_shift. 3733 */ 3734static boolean_t 3735arc_is_overflowing(void) 3736{ 3737 /* Always allow at least one block of overflow */ 3738 uint64_t overflow = MAX(SPA_MAXBLOCKSIZE, 3739 arc_c >> zfs_arc_overflow_shift); 3740 3741 return (arc_size >= arc_c + overflow); 3742} 3743 3744/* 3745 * The buffer, supplied as the first argument, needs a data block. If we 3746 * are hitting the hard limit for the cache size, we must sleep, waiting 3747 * for the eviction thread to catch up. If we're past the target size 3748 * but below the hard limit, we'll only signal the reclaim thread and 3749 * continue on. 3750 */ 3751static void 3752arc_get_data_buf(arc_buf_t *buf) 3753{ 3754 arc_state_t *state = buf->b_hdr->b_l1hdr.b_state; 3755 uint64_t size = buf->b_hdr->b_size; 3756 arc_buf_contents_t type = arc_buf_type(buf->b_hdr); 3757 3758 arc_adapt(size, state); 3759 3760 /* 3761 * If arc_size is currently overflowing, and has grown past our 3762 * upper limit, we must be adding data faster than the evict 3763 * thread can evict. Thus, to ensure we don't compound the 3764 * problem by adding more data and forcing arc_size to grow even 3765 * further past it's target size, we halt and wait for the 3766 * eviction thread to catch up. 3767 * 3768 * It's also possible that the reclaim thread is unable to evict 3769 * enough buffers to get arc_size below the overflow limit (e.g. 3770 * due to buffers being un-evictable, or hash lock collisions). 3771 * In this case, we want to proceed regardless if we're 3772 * overflowing; thus we don't use a while loop here. 3773 */ 3774 if (arc_is_overflowing()) { 3775 mutex_enter(&arc_reclaim_lock); 3776 3777 /* 3778 * Now that we've acquired the lock, we may no longer be 3779 * over the overflow limit, lets check. 3780 * 3781 * We're ignoring the case of spurious wake ups. If that 3782 * were to happen, it'd let this thread consume an ARC 3783 * buffer before it should have (i.e. before we're under 3784 * the overflow limit and were signalled by the reclaim 3785 * thread). As long as that is a rare occurrence, it 3786 * shouldn't cause any harm. 3787 */ 3788 if (arc_is_overflowing()) { 3789 cv_signal(&arc_reclaim_thread_cv); 3790 cv_wait(&arc_reclaim_waiters_cv, &arc_reclaim_lock); 3791 } 3792 3793 mutex_exit(&arc_reclaim_lock); 3794 } 3795 3796 if (type == ARC_BUFC_METADATA) { 3797 buf->b_data = zio_buf_alloc(size); 3798 arc_space_consume(size, ARC_SPACE_META); 3799 } else { 3800 ASSERT(type == ARC_BUFC_DATA); 3801 buf->b_data = zio_data_buf_alloc(size); 3802 arc_space_consume(size, ARC_SPACE_DATA); 3803 } 3804 3805 /* 3806 * Update the state size. Note that ghost states have a 3807 * "ghost size" and so don't need to be updated. 3808 */ 3809 if (!GHOST_STATE(buf->b_hdr->b_l1hdr.b_state)) { 3810 arc_buf_hdr_t *hdr = buf->b_hdr; 3811 3812 atomic_add_64(&hdr->b_l1hdr.b_state->arcs_size, size); 3813 3814 /* 3815 * If this is reached via arc_read, the link is 3816 * protected by the hash lock. If reached via 3817 * arc_buf_alloc, the header should not be accessed by 3818 * any other thread. And, if reached via arc_read_done, 3819 * the hash lock will protect it if it's found in the 3820 * hash table; otherwise no other thread should be 3821 * trying to [add|remove]_reference it. 3822 */ 3823 if (multilist_link_active(&hdr->b_l1hdr.b_arc_node)) { 3824 ASSERT(refcount_is_zero(&hdr->b_l1hdr.b_refcnt)); 3825 atomic_add_64(&hdr->b_l1hdr.b_state->arcs_lsize[type], 3826 size); 3827 } 3828 /* 3829 * If we are growing the cache, and we are adding anonymous 3830 * data, and we have outgrown arc_p, update arc_p 3831 */ 3832 if (arc_size < arc_c && hdr->b_l1hdr.b_state == arc_anon && 3833 arc_anon->arcs_size + arc_mru->arcs_size > arc_p) 3834 arc_p = MIN(arc_c, arc_p + size); 3835 } 3836 ARCSTAT_BUMP(arcstat_allocated); 3837} 3838 3839/* 3840 * This routine is called whenever a buffer is accessed. 3841 * NOTE: the hash lock is dropped in this function. 3842 */ 3843static void 3844arc_access(arc_buf_hdr_t *hdr, kmutex_t *hash_lock) 3845{ 3846 clock_t now; 3847 3848 ASSERT(MUTEX_HELD(hash_lock)); 3849 ASSERT(HDR_HAS_L1HDR(hdr)); 3850 3851 if (hdr->b_l1hdr.b_state == arc_anon) { 3852 /* 3853 * This buffer is not in the cache, and does not 3854 * appear in our "ghost" list. Add the new buffer 3855 * to the MRU state. 3856 */ 3857 3858 ASSERT0(hdr->b_l1hdr.b_arc_access); 3859 hdr->b_l1hdr.b_arc_access = ddi_get_lbolt(); 3860 DTRACE_PROBE1(new_state__mru, arc_buf_hdr_t *, hdr); 3861 arc_change_state(arc_mru, hdr, hash_lock); 3862 3863 } else if (hdr->b_l1hdr.b_state == arc_mru) { 3864 now = ddi_get_lbolt(); 3865 3866 /* 3867 * If this buffer is here because of a prefetch, then either: 3868 * - clear the flag if this is a "referencing" read 3869 * (any subsequent access will bump this into the MFU state). 3870 * or 3871 * - move the buffer to the head of the list if this is 3872 * another prefetch (to make it less likely to be evicted). 3873 */ 3874 if (HDR_PREFETCH(hdr)) { 3875 if (refcount_count(&hdr->b_l1hdr.b_refcnt) == 0) { 3876 /* link protected by hash lock */ 3877 ASSERT(multilist_link_active( 3878 &hdr->b_l1hdr.b_arc_node)); 3879 } else { 3880 hdr->b_flags &= ~ARC_FLAG_PREFETCH; 3881 ARCSTAT_BUMP(arcstat_mru_hits); 3882 } 3883 hdr->b_l1hdr.b_arc_access = now; 3884 return; 3885 } 3886 3887 /* 3888 * This buffer has been "accessed" only once so far, 3889 * but it is still in the cache. Move it to the MFU 3890 * state. 3891 */ 3892 if (now > hdr->b_l1hdr.b_arc_access + ARC_MINTIME) { 3893 /* 3894 * More than 125ms have passed since we 3895 * instantiated this buffer. Move it to the 3896 * most frequently used state. 3897 */ 3898 hdr->b_l1hdr.b_arc_access = now; 3899 DTRACE_PROBE1(new_state__mfu, arc_buf_hdr_t *, hdr); 3900 arc_change_state(arc_mfu, hdr, hash_lock); 3901 } 3902 ARCSTAT_BUMP(arcstat_mru_hits); 3903 } else if (hdr->b_l1hdr.b_state == arc_mru_ghost) { 3904 arc_state_t *new_state; 3905 /* 3906 * This buffer has been "accessed" recently, but 3907 * was evicted from the cache. Move it to the 3908 * MFU state. 3909 */ 3910 3911 if (HDR_PREFETCH(hdr)) { 3912 new_state = arc_mru; 3913 if (refcount_count(&hdr->b_l1hdr.b_refcnt) > 0) 3914 hdr->b_flags &= ~ARC_FLAG_PREFETCH; 3915 DTRACE_PROBE1(new_state__mru, arc_buf_hdr_t *, hdr); 3916 } else { 3917 new_state = arc_mfu; 3918 DTRACE_PROBE1(new_state__mfu, arc_buf_hdr_t *, hdr); 3919 } 3920 3921 hdr->b_l1hdr.b_arc_access = ddi_get_lbolt(); 3922 arc_change_state(new_state, hdr, hash_lock); 3923 3924 ARCSTAT_BUMP(arcstat_mru_ghost_hits); 3925 } else if (hdr->b_l1hdr.b_state == arc_mfu) { 3926 /* 3927 * This buffer has been accessed more than once and is 3928 * still in the cache. Keep it in the MFU state. 3929 * 3930 * NOTE: an add_reference() that occurred when we did 3931 * the arc_read() will have kicked this off the list. 3932 * If it was a prefetch, we will explicitly move it to 3933 * the head of the list now. 3934 */ 3935 if ((HDR_PREFETCH(hdr)) != 0) { 3936 ASSERT(refcount_is_zero(&hdr->b_l1hdr.b_refcnt)); 3937 /* link protected by hash_lock */ 3938 ASSERT(multilist_link_active(&hdr->b_l1hdr.b_arc_node)); 3939 } 3940 ARCSTAT_BUMP(arcstat_mfu_hits); 3941 hdr->b_l1hdr.b_arc_access = ddi_get_lbolt(); 3942 } else if (hdr->b_l1hdr.b_state == arc_mfu_ghost) { 3943 arc_state_t *new_state = arc_mfu; 3944 /* 3945 * This buffer has been accessed more than once but has 3946 * been evicted from the cache. Move it back to the 3947 * MFU state. 3948 */ 3949 3950 if (HDR_PREFETCH(hdr)) { 3951 /* 3952 * This is a prefetch access... 3953 * move this block back to the MRU state. 3954 */ 3955 ASSERT0(refcount_count(&hdr->b_l1hdr.b_refcnt)); 3956 new_state = arc_mru; 3957 } 3958 3959 hdr->b_l1hdr.b_arc_access = ddi_get_lbolt(); 3960 DTRACE_PROBE1(new_state__mfu, arc_buf_hdr_t *, hdr); 3961 arc_change_state(new_state, hdr, hash_lock); 3962 3963 ARCSTAT_BUMP(arcstat_mfu_ghost_hits); 3964 } else if (hdr->b_l1hdr.b_state == arc_l2c_only) { 3965 /* 3966 * This buffer is on the 2nd Level ARC. 3967 */ 3968 3969 hdr->b_l1hdr.b_arc_access = ddi_get_lbolt(); 3970 DTRACE_PROBE1(new_state__mfu, arc_buf_hdr_t *, hdr); 3971 arc_change_state(arc_mfu, hdr, hash_lock); 3972 } else { 3973 ASSERT(!"invalid arc state"); 3974 } 3975} 3976 3977/* a generic arc_done_func_t which you can use */ 3978/* ARGSUSED */ 3979void 3980arc_bcopy_func(zio_t *zio, arc_buf_t *buf, void *arg) 3981{ 3982 if (zio == NULL || zio->io_error == 0) 3983 bcopy(buf->b_data, arg, buf->b_hdr->b_size); 3984 VERIFY(arc_buf_remove_ref(buf, arg)); 3985} 3986 3987/* a generic arc_done_func_t */ 3988void 3989arc_getbuf_func(zio_t *zio, arc_buf_t *buf, void *arg) 3990{ 3991 arc_buf_t **bufp = arg; 3992 if (zio && zio->io_error) { 3993 VERIFY(arc_buf_remove_ref(buf, arg)); 3994 *bufp = NULL; 3995 } else { 3996 *bufp = buf; 3997 ASSERT(buf->b_data); 3998 } 3999} 4000 4001static void 4002arc_read_done(zio_t *zio) 4003{ 4004 arc_buf_hdr_t *hdr; 4005 arc_buf_t *buf; 4006 arc_buf_t *abuf; /* buffer we're assigning to callback */ 4007 kmutex_t *hash_lock = NULL; 4008 arc_callback_t *callback_list, *acb; 4009 int freeable = FALSE; 4010 4011 buf = zio->io_private; 4012 hdr = buf->b_hdr; 4013 4014 /* 4015 * The hdr was inserted into hash-table and removed from lists 4016 * prior to starting I/O. We should find this header, since 4017 * it's in the hash table, and it should be legit since it's 4018 * not possible to evict it during the I/O. The only possible 4019 * reason for it not to be found is if we were freed during the 4020 * read. 4021 */ 4022 if (HDR_IN_HASH_TABLE(hdr)) { 4023 ASSERT3U(hdr->b_birth, ==, BP_PHYSICAL_BIRTH(zio->io_bp)); 4024 ASSERT3U(hdr->b_dva.dva_word[0], ==, 4025 BP_IDENTITY(zio->io_bp)->dva_word[0]); 4026 ASSERT3U(hdr->b_dva.dva_word[1], ==, 4027 BP_IDENTITY(zio->io_bp)->dva_word[1]); 4028 4029 arc_buf_hdr_t *found = buf_hash_find(hdr->b_spa, zio->io_bp, 4030 &hash_lock); 4031 4032 ASSERT((found == NULL && HDR_FREED_IN_READ(hdr) && 4033 hash_lock == NULL) || 4034 (found == hdr && 4035 DVA_EQUAL(&hdr->b_dva, BP_IDENTITY(zio->io_bp))) || 4036 (found == hdr && HDR_L2_READING(hdr))); 4037 } 4038 4039 hdr->b_flags &= ~ARC_FLAG_L2_EVICTED; 4040 if (l2arc_noprefetch && HDR_PREFETCH(hdr)) 4041 hdr->b_flags &= ~ARC_FLAG_L2CACHE; 4042 4043 /* byteswap if necessary */ 4044 callback_list = hdr->b_l1hdr.b_acb; 4045 ASSERT(callback_list != NULL); 4046 if (BP_SHOULD_BYTESWAP(zio->io_bp) && zio->io_error == 0) { 4047 dmu_object_byteswap_t bswap = 4048 DMU_OT_BYTESWAP(BP_GET_TYPE(zio->io_bp)); 4049 arc_byteswap_func_t *func = BP_GET_LEVEL(zio->io_bp) > 0 ? 4050 byteswap_uint64_array : 4051 dmu_ot_byteswap[bswap].ob_func; 4052 func(buf->b_data, hdr->b_size); 4053 } 4054 4055 arc_cksum_compute(buf, B_FALSE); 4056#ifdef illumos 4057 arc_buf_watch(buf); 4058#endif /* illumos */ 4059 4060 if (hash_lock && zio->io_error == 0 && 4061 hdr->b_l1hdr.b_state == arc_anon) { 4062 /* 4063 * Only call arc_access on anonymous buffers. This is because 4064 * if we've issued an I/O for an evicted buffer, we've already 4065 * called arc_access (to prevent any simultaneous readers from 4066 * getting confused). 4067 */ 4068 arc_access(hdr, hash_lock); 4069 } 4070 4071 /* create copies of the data buffer for the callers */ 4072 abuf = buf; 4073 for (acb = callback_list; acb; acb = acb->acb_next) { 4074 if (acb->acb_done) { 4075 if (abuf == NULL) { 4076 ARCSTAT_BUMP(arcstat_duplicate_reads); 4077 abuf = arc_buf_clone(buf); 4078 } 4079 acb->acb_buf = abuf; 4080 abuf = NULL; 4081 } 4082 } 4083 hdr->b_l1hdr.b_acb = NULL; 4084 hdr->b_flags &= ~ARC_FLAG_IO_IN_PROGRESS; 4085 ASSERT(!HDR_BUF_AVAILABLE(hdr)); 4086 if (abuf == buf) { 4087 ASSERT(buf->b_efunc == NULL); 4088 ASSERT(hdr->b_l1hdr.b_datacnt == 1); 4089 hdr->b_flags |= ARC_FLAG_BUF_AVAILABLE; 4090 } 4091 4092 ASSERT(refcount_is_zero(&hdr->b_l1hdr.b_refcnt) || 4093 callback_list != NULL); 4094 4095 if (zio->io_error != 0) { 4096 hdr->b_flags |= ARC_FLAG_IO_ERROR; 4097 if (hdr->b_l1hdr.b_state != arc_anon) 4098 arc_change_state(arc_anon, hdr, hash_lock); 4099 if (HDR_IN_HASH_TABLE(hdr)) 4100 buf_hash_remove(hdr); 4101 freeable = refcount_is_zero(&hdr->b_l1hdr.b_refcnt); 4102 } 4103 4104 /* 4105 * Broadcast before we drop the hash_lock to avoid the possibility 4106 * that the hdr (and hence the cv) might be freed before we get to 4107 * the cv_broadcast(). 4108 */ 4109 cv_broadcast(&hdr->b_l1hdr.b_cv); 4110 4111 if (hash_lock != NULL) { 4112 mutex_exit(hash_lock); 4113 } else { 4114 /* 4115 * This block was freed while we waited for the read to 4116 * complete. It has been removed from the hash table and 4117 * moved to the anonymous state (so that it won't show up 4118 * in the cache). 4119 */ 4120 ASSERT3P(hdr->b_l1hdr.b_state, ==, arc_anon); 4121 freeable = refcount_is_zero(&hdr->b_l1hdr.b_refcnt); 4122 } 4123 4124 /* execute each callback and free its structure */ 4125 while ((acb = callback_list) != NULL) { 4126 if (acb->acb_done) 4127 acb->acb_done(zio, acb->acb_buf, acb->acb_private); 4128 4129 if (acb->acb_zio_dummy != NULL) { 4130 acb->acb_zio_dummy->io_error = zio->io_error; 4131 zio_nowait(acb->acb_zio_dummy); 4132 } 4133 4134 callback_list = acb->acb_next; 4135 kmem_free(acb, sizeof (arc_callback_t)); 4136 } 4137 4138 if (freeable) 4139 arc_hdr_destroy(hdr); 4140} 4141 4142/* 4143 * "Read" the block at the specified DVA (in bp) via the 4144 * cache. If the block is found in the cache, invoke the provided 4145 * callback immediately and return. Note that the `zio' parameter 4146 * in the callback will be NULL in this case, since no IO was 4147 * required. If the block is not in the cache pass the read request 4148 * on to the spa with a substitute callback function, so that the 4149 * requested block will be added to the cache. 4150 * 4151 * If a read request arrives for a block that has a read in-progress, 4152 * either wait for the in-progress read to complete (and return the 4153 * results); or, if this is a read with a "done" func, add a record 4154 * to the read to invoke the "done" func when the read completes, 4155 * and return; or just return. 4156 * 4157 * arc_read_done() will invoke all the requested "done" functions 4158 * for readers of this block. 4159 */ 4160int 4161arc_read(zio_t *pio, spa_t *spa, const blkptr_t *bp, arc_done_func_t *done, 4162 void *private, zio_priority_t priority, int zio_flags, 4163 arc_flags_t *arc_flags, const zbookmark_phys_t *zb) 4164{ 4165 arc_buf_hdr_t *hdr = NULL; 4166 arc_buf_t *buf = NULL; 4167 kmutex_t *hash_lock = NULL; 4168 zio_t *rzio; 4169 uint64_t guid = spa_load_guid(spa); 4170 4171 ASSERT(!BP_IS_EMBEDDED(bp) || 4172 BPE_GET_ETYPE(bp) == BP_EMBEDDED_TYPE_DATA); 4173 4174top: 4175 if (!BP_IS_EMBEDDED(bp)) { 4176 /* 4177 * Embedded BP's have no DVA and require no I/O to "read". 4178 * Create an anonymous arc buf to back it. 4179 */ 4180 hdr = buf_hash_find(guid, bp, &hash_lock); 4181 } 4182 4183 if (hdr != NULL && HDR_HAS_L1HDR(hdr) && hdr->b_l1hdr.b_datacnt > 0) { 4184 4185 *arc_flags |= ARC_FLAG_CACHED; 4186 4187 if (HDR_IO_IN_PROGRESS(hdr)) { 4188 4189 if (*arc_flags & ARC_FLAG_WAIT) { 4190 cv_wait(&hdr->b_l1hdr.b_cv, hash_lock); 4191 mutex_exit(hash_lock); 4192 goto top; 4193 } 4194 ASSERT(*arc_flags & ARC_FLAG_NOWAIT); 4195 4196 if (done) { 4197 arc_callback_t *acb = NULL; 4198 4199 acb = kmem_zalloc(sizeof (arc_callback_t), 4200 KM_SLEEP); 4201 acb->acb_done = done; 4202 acb->acb_private = private; 4203 if (pio != NULL) 4204 acb->acb_zio_dummy = zio_null(pio, 4205 spa, NULL, NULL, NULL, zio_flags); 4206 4207 ASSERT(acb->acb_done != NULL); 4208 acb->acb_next = hdr->b_l1hdr.b_acb; 4209 hdr->b_l1hdr.b_acb = acb; 4210 add_reference(hdr, hash_lock, private); 4211 mutex_exit(hash_lock); 4212 return (0); 4213 } 4214 mutex_exit(hash_lock); 4215 return (0); 4216 } 4217 4218 ASSERT(hdr->b_l1hdr.b_state == arc_mru || 4219 hdr->b_l1hdr.b_state == arc_mfu); 4220 4221 if (done) { 4222 add_reference(hdr, hash_lock, private); 4223 /* 4224 * If this block is already in use, create a new 4225 * copy of the data so that we will be guaranteed 4226 * that arc_release() will always succeed. 4227 */ 4228 buf = hdr->b_l1hdr.b_buf; 4229 ASSERT(buf); 4230 ASSERT(buf->b_data); 4231 if (HDR_BUF_AVAILABLE(hdr)) { 4232 ASSERT(buf->b_efunc == NULL); 4233 hdr->b_flags &= ~ARC_FLAG_BUF_AVAILABLE; 4234 } else { 4235 buf = arc_buf_clone(buf); 4236 } 4237 4238 } else if (*arc_flags & ARC_FLAG_PREFETCH && 4239 refcount_count(&hdr->b_l1hdr.b_refcnt) == 0) { 4240 hdr->b_flags |= ARC_FLAG_PREFETCH; 4241 } 4242 DTRACE_PROBE1(arc__hit, arc_buf_hdr_t *, hdr); 4243 arc_access(hdr, hash_lock); 4244 if (*arc_flags & ARC_FLAG_L2CACHE) 4245 hdr->b_flags |= ARC_FLAG_L2CACHE; 4246 if (*arc_flags & ARC_FLAG_L2COMPRESS) 4247 hdr->b_flags |= ARC_FLAG_L2COMPRESS; 4248 mutex_exit(hash_lock); 4249 ARCSTAT_BUMP(arcstat_hits); 4250 ARCSTAT_CONDSTAT(!HDR_PREFETCH(hdr), 4251 demand, prefetch, !HDR_ISTYPE_METADATA(hdr), 4252 data, metadata, hits); 4253 4254 if (done) 4255 done(NULL, buf, private); 4256 } else { 4257 uint64_t size = BP_GET_LSIZE(bp); 4258 arc_callback_t *acb; 4259 vdev_t *vd = NULL; 4260 uint64_t addr = 0; 4261 boolean_t devw = B_FALSE; 4262 enum zio_compress b_compress = ZIO_COMPRESS_OFF; 4263 int32_t b_asize = 0; 4264 4265 if (hdr == NULL) { 4266 /* this block is not in the cache */ 4267 arc_buf_hdr_t *exists = NULL; 4268 arc_buf_contents_t type = BP_GET_BUFC_TYPE(bp); 4269 buf = arc_buf_alloc(spa, size, private, type); 4270 hdr = buf->b_hdr; 4271 if (!BP_IS_EMBEDDED(bp)) { 4272 hdr->b_dva = *BP_IDENTITY(bp); 4273 hdr->b_birth = BP_PHYSICAL_BIRTH(bp); 4274 exists = buf_hash_insert(hdr, &hash_lock); 4275 } 4276 if (exists != NULL) { 4277 /* somebody beat us to the hash insert */ 4278 mutex_exit(hash_lock); 4279 buf_discard_identity(hdr); 4280 (void) arc_buf_remove_ref(buf, private); 4281 goto top; /* restart the IO request */ 4282 } 4283 4284 /* if this is a prefetch, we don't have a reference */ 4285 if (*arc_flags & ARC_FLAG_PREFETCH) { 4286 (void) remove_reference(hdr, hash_lock, 4287 private); 4288 hdr->b_flags |= ARC_FLAG_PREFETCH; 4289 } 4290 if (*arc_flags & ARC_FLAG_L2CACHE) 4291 hdr->b_flags |= ARC_FLAG_L2CACHE; 4292 if (*arc_flags & ARC_FLAG_L2COMPRESS) 4293 hdr->b_flags |= ARC_FLAG_L2COMPRESS; 4294 if (BP_GET_LEVEL(bp) > 0) 4295 hdr->b_flags |= ARC_FLAG_INDIRECT; 4296 } else { 4297 /* 4298 * This block is in the ghost cache. If it was L2-only 4299 * (and thus didn't have an L1 hdr), we realloc the 4300 * header to add an L1 hdr. 4301 */ 4302 if (!HDR_HAS_L1HDR(hdr)) { 4303 hdr = arc_hdr_realloc(hdr, hdr_l2only_cache, 4304 hdr_full_cache); 4305 } 4306 4307 ASSERT(GHOST_STATE(hdr->b_l1hdr.b_state)); 4308 ASSERT(!HDR_IO_IN_PROGRESS(hdr)); 4309 ASSERT(refcount_is_zero(&hdr->b_l1hdr.b_refcnt)); 4310 ASSERT3P(hdr->b_l1hdr.b_buf, ==, NULL); 4311 4312 /* if this is a prefetch, we don't have a reference */ 4313 if (*arc_flags & ARC_FLAG_PREFETCH) 4314 hdr->b_flags |= ARC_FLAG_PREFETCH; 4315 else 4316 add_reference(hdr, hash_lock, private); 4317 if (*arc_flags & ARC_FLAG_L2CACHE) 4318 hdr->b_flags |= ARC_FLAG_L2CACHE; 4319 if (*arc_flags & ARC_FLAG_L2COMPRESS) 4320 hdr->b_flags |= ARC_FLAG_L2COMPRESS; 4321 buf = kmem_cache_alloc(buf_cache, KM_PUSHPAGE); 4322 buf->b_hdr = hdr; 4323 buf->b_data = NULL; 4324 buf->b_efunc = NULL; 4325 buf->b_private = NULL; 4326 buf->b_next = NULL; 4327 hdr->b_l1hdr.b_buf = buf; 4328 ASSERT0(hdr->b_l1hdr.b_datacnt); 4329 hdr->b_l1hdr.b_datacnt = 1; 4330 arc_get_data_buf(buf); 4331 arc_access(hdr, hash_lock); 4332 } 4333 4334 ASSERT(!GHOST_STATE(hdr->b_l1hdr.b_state)); 4335 4336 acb = kmem_zalloc(sizeof (arc_callback_t), KM_SLEEP); 4337 acb->acb_done = done; 4338 acb->acb_private = private; 4339 4340 ASSERT(hdr->b_l1hdr.b_acb == NULL); 4341 hdr->b_l1hdr.b_acb = acb; 4342 hdr->b_flags |= ARC_FLAG_IO_IN_PROGRESS; 4343 4344 if (HDR_HAS_L2HDR(hdr) && 4345 (vd = hdr->b_l2hdr.b_dev->l2ad_vdev) != NULL) { 4346 devw = hdr->b_l2hdr.b_dev->l2ad_writing; 4347 addr = hdr->b_l2hdr.b_daddr; 4348 b_compress = HDR_GET_COMPRESS(hdr); 4349 b_asize = hdr->b_l2hdr.b_asize; 4350 /* 4351 * Lock out device removal. 4352 */ 4353 if (vdev_is_dead(vd) || 4354 !spa_config_tryenter(spa, SCL_L2ARC, vd, RW_READER)) 4355 vd = NULL; 4356 } 4357 4358 if (hash_lock != NULL) 4359 mutex_exit(hash_lock); 4360 4361 /* 4362 * At this point, we have a level 1 cache miss. Try again in 4363 * L2ARC if possible. 4364 */ 4365 ASSERT3U(hdr->b_size, ==, size); 4366 DTRACE_PROBE4(arc__miss, arc_buf_hdr_t *, hdr, blkptr_t *, bp, 4367 uint64_t, size, zbookmark_phys_t *, zb); 4368 ARCSTAT_BUMP(arcstat_misses); 4369 ARCSTAT_CONDSTAT(!HDR_PREFETCH(hdr), 4370 demand, prefetch, !HDR_ISTYPE_METADATA(hdr), 4371 data, metadata, misses); 4372#ifdef _KERNEL 4373 curthread->td_ru.ru_inblock++; 4374#endif 4375 4376 if (vd != NULL && l2arc_ndev != 0 && !(l2arc_norw && devw)) { 4377 /* 4378 * Read from the L2ARC if the following are true: 4379 * 1. The L2ARC vdev was previously cached. 4380 * 2. This buffer still has L2ARC metadata. 4381 * 3. This buffer isn't currently writing to the L2ARC. 4382 * 4. The L2ARC entry wasn't evicted, which may 4383 * also have invalidated the vdev. 4384 * 5. This isn't prefetch and l2arc_noprefetch is set. 4385 */ 4386 if (HDR_HAS_L2HDR(hdr) && 4387 !HDR_L2_WRITING(hdr) && !HDR_L2_EVICTED(hdr) && 4388 !(l2arc_noprefetch && HDR_PREFETCH(hdr))) { 4389 l2arc_read_callback_t *cb; 4390 4391 DTRACE_PROBE1(l2arc__hit, arc_buf_hdr_t *, hdr); 4392 ARCSTAT_BUMP(arcstat_l2_hits); 4393 4394 cb = kmem_zalloc(sizeof (l2arc_read_callback_t), 4395 KM_SLEEP); 4396 cb->l2rcb_buf = buf; 4397 cb->l2rcb_spa = spa; 4398 cb->l2rcb_bp = *bp; 4399 cb->l2rcb_zb = *zb; 4400 cb->l2rcb_flags = zio_flags; 4401 cb->l2rcb_compress = b_compress; 4402 4403 ASSERT(addr >= VDEV_LABEL_START_SIZE && 4404 addr + size < vd->vdev_psize - 4405 VDEV_LABEL_END_SIZE); 4406 4407 /* 4408 * l2arc read. The SCL_L2ARC lock will be 4409 * released by l2arc_read_done(). 4410 * Issue a null zio if the underlying buffer 4411 * was squashed to zero size by compression. 4412 */ 4413 if (b_compress == ZIO_COMPRESS_EMPTY) { 4414 rzio = zio_null(pio, spa, vd, 4415 l2arc_read_done, cb, 4416 zio_flags | ZIO_FLAG_DONT_CACHE | 4417 ZIO_FLAG_CANFAIL | 4418 ZIO_FLAG_DONT_PROPAGATE | 4419 ZIO_FLAG_DONT_RETRY); 4420 } else { 4421 rzio = zio_read_phys(pio, vd, addr, 4422 b_asize, buf->b_data, 4423 ZIO_CHECKSUM_OFF, 4424 l2arc_read_done, cb, priority, 4425 zio_flags | ZIO_FLAG_DONT_CACHE | 4426 ZIO_FLAG_CANFAIL | 4427 ZIO_FLAG_DONT_PROPAGATE | 4428 ZIO_FLAG_DONT_RETRY, B_FALSE); 4429 } 4430 DTRACE_PROBE2(l2arc__read, vdev_t *, vd, 4431 zio_t *, rzio); 4432 ARCSTAT_INCR(arcstat_l2_read_bytes, b_asize); 4433 4434 if (*arc_flags & ARC_FLAG_NOWAIT) { 4435 zio_nowait(rzio); 4436 return (0); 4437 } 4438 4439 ASSERT(*arc_flags & ARC_FLAG_WAIT); 4440 if (zio_wait(rzio) == 0) 4441 return (0); 4442 4443 /* l2arc read error; goto zio_read() */ 4444 } else { 4445 DTRACE_PROBE1(l2arc__miss, 4446 arc_buf_hdr_t *, hdr); 4447 ARCSTAT_BUMP(arcstat_l2_misses); 4448 if (HDR_L2_WRITING(hdr)) 4449 ARCSTAT_BUMP(arcstat_l2_rw_clash); 4450 spa_config_exit(spa, SCL_L2ARC, vd); 4451 } 4452 } else { 4453 if (vd != NULL) 4454 spa_config_exit(spa, SCL_L2ARC, vd); 4455 if (l2arc_ndev != 0) { 4456 DTRACE_PROBE1(l2arc__miss, 4457 arc_buf_hdr_t *, hdr); 4458 ARCSTAT_BUMP(arcstat_l2_misses); 4459 } 4460 } 4461 4462 rzio = zio_read(pio, spa, bp, buf->b_data, size, 4463 arc_read_done, buf, priority, zio_flags, zb); 4464 4465 if (*arc_flags & ARC_FLAG_WAIT) 4466 return (zio_wait(rzio)); 4467 4468 ASSERT(*arc_flags & ARC_FLAG_NOWAIT); 4469 zio_nowait(rzio); 4470 } 4471 return (0); 4472} 4473 4474void 4475arc_set_callback(arc_buf_t *buf, arc_evict_func_t *func, void *private) 4476{ 4477 ASSERT(buf->b_hdr != NULL); 4478 ASSERT(buf->b_hdr->b_l1hdr.b_state != arc_anon); 4479 ASSERT(!refcount_is_zero(&buf->b_hdr->b_l1hdr.b_refcnt) || 4480 func == NULL); 4481 ASSERT(buf->b_efunc == NULL); 4482 ASSERT(!HDR_BUF_AVAILABLE(buf->b_hdr)); 4483 4484 buf->b_efunc = func; 4485 buf->b_private = private; 4486} 4487 4488/* 4489 * Notify the arc that a block was freed, and thus will never be used again. 4490 */ 4491void 4492arc_freed(spa_t *spa, const blkptr_t *bp) 4493{ 4494 arc_buf_hdr_t *hdr; 4495 kmutex_t *hash_lock; 4496 uint64_t guid = spa_load_guid(spa); 4497 4498 ASSERT(!BP_IS_EMBEDDED(bp)); 4499 4500 hdr = buf_hash_find(guid, bp, &hash_lock); 4501 if (hdr == NULL) 4502 return; 4503 if (HDR_BUF_AVAILABLE(hdr)) { 4504 arc_buf_t *buf = hdr->b_l1hdr.b_buf; 4505 add_reference(hdr, hash_lock, FTAG); 4506 hdr->b_flags &= ~ARC_FLAG_BUF_AVAILABLE; 4507 mutex_exit(hash_lock); 4508 4509 arc_release(buf, FTAG); 4510 (void) arc_buf_remove_ref(buf, FTAG); 4511 } else { 4512 mutex_exit(hash_lock); 4513 } 4514 4515} 4516 4517/* 4518 * Clear the user eviction callback set by arc_set_callback(), first calling 4519 * it if it exists. Because the presence of a callback keeps an arc_buf cached 4520 * clearing the callback may result in the arc_buf being destroyed. However, 4521 * it will not result in the *last* arc_buf being destroyed, hence the data 4522 * will remain cached in the ARC. We make a copy of the arc buffer here so 4523 * that we can process the callback without holding any locks. 4524 * 4525 * It's possible that the callback is already in the process of being cleared 4526 * by another thread. In this case we can not clear the callback. 4527 * 4528 * Returns B_TRUE if the callback was successfully called and cleared. 4529 */ 4530boolean_t 4531arc_clear_callback(arc_buf_t *buf) 4532{ 4533 arc_buf_hdr_t *hdr; 4534 kmutex_t *hash_lock; 4535 arc_evict_func_t *efunc = buf->b_efunc; 4536 void *private = buf->b_private; 4537 4538 mutex_enter(&buf->b_evict_lock); 4539 hdr = buf->b_hdr; 4540 if (hdr == NULL) { 4541 /* 4542 * We are in arc_do_user_evicts(). 4543 */ 4544 ASSERT(buf->b_data == NULL); 4545 mutex_exit(&buf->b_evict_lock); 4546 return (B_FALSE); 4547 } else if (buf->b_data == NULL) { 4548 /* 4549 * We are on the eviction list; process this buffer now 4550 * but let arc_do_user_evicts() do the reaping. 4551 */ 4552 buf->b_efunc = NULL; 4553 mutex_exit(&buf->b_evict_lock); 4554 VERIFY0(efunc(private)); 4555 return (B_TRUE); 4556 } 4557 hash_lock = HDR_LOCK(hdr); 4558 mutex_enter(hash_lock); 4559 hdr = buf->b_hdr; 4560 ASSERT3P(hash_lock, ==, HDR_LOCK(hdr)); 4561 4562 ASSERT3U(refcount_count(&hdr->b_l1hdr.b_refcnt), <, 4563 hdr->b_l1hdr.b_datacnt); 4564 ASSERT(hdr->b_l1hdr.b_state == arc_mru || 4565 hdr->b_l1hdr.b_state == arc_mfu); 4566 4567 buf->b_efunc = NULL; 4568 buf->b_private = NULL; 4569 4570 if (hdr->b_l1hdr.b_datacnt > 1) { 4571 mutex_exit(&buf->b_evict_lock); 4572 arc_buf_destroy(buf, TRUE); 4573 } else { 4574 ASSERT(buf == hdr->b_l1hdr.b_buf); 4575 hdr->b_flags |= ARC_FLAG_BUF_AVAILABLE; 4576 mutex_exit(&buf->b_evict_lock); 4577 } 4578 4579 mutex_exit(hash_lock); 4580 VERIFY0(efunc(private)); 4581 return (B_TRUE); 4582} 4583 4584/* 4585 * Release this buffer from the cache, making it an anonymous buffer. This 4586 * must be done after a read and prior to modifying the buffer contents. 4587 * If the buffer has more than one reference, we must make 4588 * a new hdr for the buffer. 4589 */ 4590void 4591arc_release(arc_buf_t *buf, void *tag) 4592{ 4593 arc_buf_hdr_t *hdr = buf->b_hdr; 4594 4595 ASSERT(HDR_HAS_L1HDR(hdr)); 4596 4597 /* 4598 * It would be nice to assert that if it's DMU metadata (level > 4599 * 0 || it's the dnode file), then it must be syncing context. 4600 * But we don't know that information at this level. 4601 */ 4602 4603 mutex_enter(&buf->b_evict_lock); 4604 /* 4605 * We don't grab the hash lock prior to this check, because if 4606 * the buffer's header is in the arc_anon state, it won't be 4607 * linked into the hash table. 4608 */ 4609 if (hdr->b_l1hdr.b_state == arc_anon) { 4610 mutex_exit(&buf->b_evict_lock); 4611 ASSERT(!HDR_IO_IN_PROGRESS(hdr)); 4612 ASSERT(!HDR_IN_HASH_TABLE(hdr)); 4613 ASSERT(!HDR_HAS_L2HDR(hdr)); 4614 ASSERT(BUF_EMPTY(hdr)); 4615 ASSERT3U(hdr->b_l1hdr.b_datacnt, ==, 1); 4616 ASSERT3S(refcount_count(&hdr->b_l1hdr.b_refcnt), ==, 1); 4617 ASSERT(!list_link_active(&hdr->b_l1hdr.b_arc_node)); 4618 4619 ASSERT3P(buf->b_efunc, ==, NULL); 4620 ASSERT3P(buf->b_private, ==, NULL); 4621 4622 hdr->b_l1hdr.b_arc_access = 0; 4623 arc_buf_thaw(buf); 4624 4625 return; 4626 } 4627 4628 kmutex_t *hash_lock = HDR_LOCK(hdr); 4629 mutex_enter(hash_lock); 4630 4631 /* 4632 * This assignment is only valid as long as the hash_lock is 4633 * held, we must be careful not to reference state or the 4634 * b_state field after dropping the lock. 4635 */ 4636 arc_state_t *state = hdr->b_l1hdr.b_state; 4637 ASSERT3P(hash_lock, ==, HDR_LOCK(hdr)); 4638 ASSERT3P(state, !=, arc_anon); 4639 4640 /* this buffer is not on any list */ 4641 ASSERT(refcount_count(&hdr->b_l1hdr.b_refcnt) > 0); 4642 4643 if (HDR_HAS_L2HDR(hdr)) { 4644 mutex_enter(&hdr->b_l2hdr.b_dev->l2ad_mtx); 4645 4646 /* 4647 * We have to recheck this conditional again now that 4648 * we're holding the l2ad_mtx to prevent a race with 4649 * another thread which might be concurrently calling 4650 * l2arc_evict(). In that case, l2arc_evict() might have 4651 * destroyed the header's L2 portion as we were waiting 4652 * to acquire the l2ad_mtx. 4653 */ 4654 if (HDR_HAS_L2HDR(hdr)) { 4655 if (hdr->b_l2hdr.b_daddr != L2ARC_ADDR_UNSET) 4656 trim_map_free(hdr->b_l2hdr.b_dev->l2ad_vdev, 4657 hdr->b_l2hdr.b_daddr, 4658 hdr->b_l2hdr.b_asize, 0); 4659 arc_hdr_l2hdr_destroy(hdr); 4660 } 4661 4662 mutex_exit(&hdr->b_l2hdr.b_dev->l2ad_mtx); 4663 } 4664 4665 /* 4666 * Do we have more than one buf? 4667 */ 4668 if (hdr->b_l1hdr.b_datacnt > 1) { 4669 arc_buf_hdr_t *nhdr; 4670 arc_buf_t **bufp; 4671 uint64_t blksz = hdr->b_size; 4672 uint64_t spa = hdr->b_spa; 4673 arc_buf_contents_t type = arc_buf_type(hdr); 4674 uint32_t flags = hdr->b_flags; 4675 4676 ASSERT(hdr->b_l1hdr.b_buf != buf || buf->b_next != NULL); 4677 /* 4678 * Pull the data off of this hdr and attach it to 4679 * a new anonymous hdr. 4680 */ 4681 (void) remove_reference(hdr, hash_lock, tag); 4682 bufp = &hdr->b_l1hdr.b_buf; 4683 while (*bufp != buf) 4684 bufp = &(*bufp)->b_next; 4685 *bufp = buf->b_next; 4686 buf->b_next = NULL; 4687 4688 ASSERT3P(state, !=, arc_l2c_only); 4689 ASSERT3U(state->arcs_size, >=, hdr->b_size); 4690 atomic_add_64(&state->arcs_size, -hdr->b_size); 4691 if (refcount_is_zero(&hdr->b_l1hdr.b_refcnt)) { 4692 ASSERT3P(state, !=, arc_l2c_only); 4693 uint64_t *size = &state->arcs_lsize[type]; 4694 ASSERT3U(*size, >=, hdr->b_size); 4695 atomic_add_64(size, -hdr->b_size); 4696 } 4697 4698 /* 4699 * We're releasing a duplicate user data buffer, update 4700 * our statistics accordingly. 4701 */ 4702 if (HDR_ISTYPE_DATA(hdr)) { 4703 ARCSTAT_BUMPDOWN(arcstat_duplicate_buffers); 4704 ARCSTAT_INCR(arcstat_duplicate_buffers_size, 4705 -hdr->b_size); 4706 } 4707 hdr->b_l1hdr.b_datacnt -= 1; 4708 arc_cksum_verify(buf); 4709#ifdef illumos 4710 arc_buf_unwatch(buf); 4711#endif /* illumos */ 4712 4713 mutex_exit(hash_lock); 4714 4715 nhdr = kmem_cache_alloc(hdr_full_cache, KM_PUSHPAGE); 4716 nhdr->b_size = blksz; 4717 nhdr->b_spa = spa; 4718 4719 nhdr->b_flags = flags & ARC_FLAG_L2_WRITING; 4720 nhdr->b_flags |= arc_bufc_to_flags(type); 4721 nhdr->b_flags |= ARC_FLAG_HAS_L1HDR; 4722 4723 nhdr->b_l1hdr.b_buf = buf; 4724 nhdr->b_l1hdr.b_datacnt = 1; 4725 nhdr->b_l1hdr.b_state = arc_anon; 4726 nhdr->b_l1hdr.b_arc_access = 0; 4727 nhdr->b_l1hdr.b_tmp_cdata = NULL; 4728 nhdr->b_freeze_cksum = NULL; 4729 4730 (void) refcount_add(&nhdr->b_l1hdr.b_refcnt, tag); 4731 buf->b_hdr = nhdr; 4732 mutex_exit(&buf->b_evict_lock); 4733 atomic_add_64(&arc_anon->arcs_size, blksz); 4734 } else { 4735 mutex_exit(&buf->b_evict_lock); 4736 ASSERT(refcount_count(&hdr->b_l1hdr.b_refcnt) == 1); 4737 /* protected by hash lock, or hdr is on arc_anon */ 4738 ASSERT(!multilist_link_active(&hdr->b_l1hdr.b_arc_node)); 4739 ASSERT(!HDR_IO_IN_PROGRESS(hdr)); 4740 arc_change_state(arc_anon, hdr, hash_lock); 4741 hdr->b_l1hdr.b_arc_access = 0; 4742 mutex_exit(hash_lock); 4743 4744 buf_discard_identity(hdr); 4745 arc_buf_thaw(buf); 4746 } 4747 buf->b_efunc = NULL; 4748 buf->b_private = NULL; 4749} 4750 4751int 4752arc_released(arc_buf_t *buf) 4753{ 4754 int released; 4755 4756 mutex_enter(&buf->b_evict_lock); 4757 released = (buf->b_data != NULL && 4758 buf->b_hdr->b_l1hdr.b_state == arc_anon); 4759 mutex_exit(&buf->b_evict_lock); 4760 return (released); 4761} 4762 4763#ifdef ZFS_DEBUG 4764int 4765arc_referenced(arc_buf_t *buf) 4766{ 4767 int referenced; 4768 4769 mutex_enter(&buf->b_evict_lock); 4770 referenced = (refcount_count(&buf->b_hdr->b_l1hdr.b_refcnt)); 4771 mutex_exit(&buf->b_evict_lock); 4772 return (referenced); 4773} 4774#endif 4775 4776static void 4777arc_write_ready(zio_t *zio) 4778{ 4779 arc_write_callback_t *callback = zio->io_private; 4780 arc_buf_t *buf = callback->awcb_buf; 4781 arc_buf_hdr_t *hdr = buf->b_hdr; 4782 4783 ASSERT(HDR_HAS_L1HDR(hdr)); 4784 ASSERT(!refcount_is_zero(&buf->b_hdr->b_l1hdr.b_refcnt)); 4785 ASSERT(hdr->b_l1hdr.b_datacnt > 0); 4786 callback->awcb_ready(zio, buf, callback->awcb_private); 4787 4788 /* 4789 * If the IO is already in progress, then this is a re-write 4790 * attempt, so we need to thaw and re-compute the cksum. 4791 * It is the responsibility of the callback to handle the 4792 * accounting for any re-write attempt. 4793 */ 4794 if (HDR_IO_IN_PROGRESS(hdr)) { 4795 mutex_enter(&hdr->b_l1hdr.b_freeze_lock); 4796 if (hdr->b_freeze_cksum != NULL) { 4797 kmem_free(hdr->b_freeze_cksum, sizeof (zio_cksum_t)); 4798 hdr->b_freeze_cksum = NULL; 4799 } 4800 mutex_exit(&hdr->b_l1hdr.b_freeze_lock); 4801 } 4802 arc_cksum_compute(buf, B_FALSE); 4803 hdr->b_flags |= ARC_FLAG_IO_IN_PROGRESS; 4804} 4805 4806/* 4807 * The SPA calls this callback for each physical write that happens on behalf 4808 * of a logical write. See the comment in dbuf_write_physdone() for details. 4809 */ 4810static void 4811arc_write_physdone(zio_t *zio) 4812{ 4813 arc_write_callback_t *cb = zio->io_private; 4814 if (cb->awcb_physdone != NULL) 4815 cb->awcb_physdone(zio, cb->awcb_buf, cb->awcb_private); 4816} 4817 4818static void 4819arc_write_done(zio_t *zio) 4820{ 4821 arc_write_callback_t *callback = zio->io_private; 4822 arc_buf_t *buf = callback->awcb_buf; 4823 arc_buf_hdr_t *hdr = buf->b_hdr; 4824 4825 ASSERT(hdr->b_l1hdr.b_acb == NULL); 4826 4827 if (zio->io_error == 0) { 4828 if (BP_IS_HOLE(zio->io_bp) || BP_IS_EMBEDDED(zio->io_bp)) { 4829 buf_discard_identity(hdr); 4830 } else { 4831 hdr->b_dva = *BP_IDENTITY(zio->io_bp); 4832 hdr->b_birth = BP_PHYSICAL_BIRTH(zio->io_bp); 4833 } 4834 } else { 4835 ASSERT(BUF_EMPTY(hdr)); 4836 } 4837 4838 /* 4839 * If the block to be written was all-zero or compressed enough to be 4840 * embedded in the BP, no write was performed so there will be no 4841 * dva/birth/checksum. The buffer must therefore remain anonymous 4842 * (and uncached). 4843 */ 4844 if (!BUF_EMPTY(hdr)) { 4845 arc_buf_hdr_t *exists; 4846 kmutex_t *hash_lock; 4847 4848 ASSERT(zio->io_error == 0); 4849 4850 arc_cksum_verify(buf); 4851 4852 exists = buf_hash_insert(hdr, &hash_lock); 4853 if (exists != NULL) { 4854 /* 4855 * This can only happen if we overwrite for 4856 * sync-to-convergence, because we remove 4857 * buffers from the hash table when we arc_free(). 4858 */ 4859 if (zio->io_flags & ZIO_FLAG_IO_REWRITE) { 4860 if (!BP_EQUAL(&zio->io_bp_orig, zio->io_bp)) 4861 panic("bad overwrite, hdr=%p exists=%p", 4862 (void *)hdr, (void *)exists); 4863 ASSERT(refcount_is_zero( 4864 &exists->b_l1hdr.b_refcnt)); 4865 arc_change_state(arc_anon, exists, hash_lock); 4866 mutex_exit(hash_lock); 4867 arc_hdr_destroy(exists); 4868 exists = buf_hash_insert(hdr, &hash_lock); 4869 ASSERT3P(exists, ==, NULL); 4870 } else if (zio->io_flags & ZIO_FLAG_NOPWRITE) { 4871 /* nopwrite */ 4872 ASSERT(zio->io_prop.zp_nopwrite); 4873 if (!BP_EQUAL(&zio->io_bp_orig, zio->io_bp)) 4874 panic("bad nopwrite, hdr=%p exists=%p", 4875 (void *)hdr, (void *)exists); 4876 } else { 4877 /* Dedup */ 4878 ASSERT(hdr->b_l1hdr.b_datacnt == 1); 4879 ASSERT(hdr->b_l1hdr.b_state == arc_anon); 4880 ASSERT(BP_GET_DEDUP(zio->io_bp)); 4881 ASSERT(BP_GET_LEVEL(zio->io_bp) == 0); 4882 } 4883 } 4884 hdr->b_flags &= ~ARC_FLAG_IO_IN_PROGRESS; 4885 /* if it's not anon, we are doing a scrub */ 4886 if (exists == NULL && hdr->b_l1hdr.b_state == arc_anon) 4887 arc_access(hdr, hash_lock); 4888 mutex_exit(hash_lock); 4889 } else { 4890 hdr->b_flags &= ~ARC_FLAG_IO_IN_PROGRESS; 4891 } 4892 4893 ASSERT(!refcount_is_zero(&hdr->b_l1hdr.b_refcnt)); 4894 callback->awcb_done(zio, buf, callback->awcb_private); 4895 4896 kmem_free(callback, sizeof (arc_write_callback_t)); 4897} 4898 4899zio_t * 4900arc_write(zio_t *pio, spa_t *spa, uint64_t txg, 4901 blkptr_t *bp, arc_buf_t *buf, boolean_t l2arc, boolean_t l2arc_compress, 4902 const zio_prop_t *zp, arc_done_func_t *ready, arc_done_func_t *physdone, 4903 arc_done_func_t *done, void *private, zio_priority_t priority, 4904 int zio_flags, const zbookmark_phys_t *zb) 4905{ 4906 arc_buf_hdr_t *hdr = buf->b_hdr; 4907 arc_write_callback_t *callback; 4908 zio_t *zio; 4909 4910 ASSERT(ready != NULL); 4911 ASSERT(done != NULL); 4912 ASSERT(!HDR_IO_ERROR(hdr)); 4913 ASSERT(!HDR_IO_IN_PROGRESS(hdr)); 4914 ASSERT(hdr->b_l1hdr.b_acb == NULL); 4915 ASSERT(hdr->b_l1hdr.b_datacnt > 0); 4916 if (l2arc) 4917 hdr->b_flags |= ARC_FLAG_L2CACHE; 4918 if (l2arc_compress) 4919 hdr->b_flags |= ARC_FLAG_L2COMPRESS; 4920 callback = kmem_zalloc(sizeof (arc_write_callback_t), KM_SLEEP); 4921 callback->awcb_ready = ready; 4922 callback->awcb_physdone = physdone; 4923 callback->awcb_done = done; 4924 callback->awcb_private = private; 4925 callback->awcb_buf = buf; 4926 4927 zio = zio_write(pio, spa, txg, bp, buf->b_data, hdr->b_size, zp, 4928 arc_write_ready, arc_write_physdone, arc_write_done, callback, 4929 priority, zio_flags, zb); 4930 4931 return (zio); 4932} 4933 4934static int 4935arc_memory_throttle(uint64_t reserve, uint64_t txg) 4936{ 4937#ifdef _KERNEL 4938 uint64_t available_memory = ptob(freemem); 4939 static uint64_t page_load = 0; 4940 static uint64_t last_txg = 0; 4941 4942#if defined(__i386) || !defined(UMA_MD_SMALL_ALLOC) 4943 available_memory = 4944 MIN(available_memory, ptob(vmem_size(heap_arena, VMEM_FREE))); 4945#endif 4946 4947 if (freemem > (uint64_t)physmem * arc_lotsfree_percent / 100) 4948 return (0); 4949 4950 if (txg > last_txg) { 4951 last_txg = txg; 4952 page_load = 0; 4953 } 4954 /* 4955 * If we are in pageout, we know that memory is already tight, 4956 * the arc is already going to be evicting, so we just want to 4957 * continue to let page writes occur as quickly as possible. 4958 */ 4959 if (curproc == pageproc) { 4960 if (page_load > MAX(ptob(minfree), available_memory) / 4) 4961 return (SET_ERROR(ERESTART)); 4962 /* Note: reserve is inflated, so we deflate */ 4963 page_load += reserve / 8; 4964 return (0); 4965 } else if (page_load > 0 && arc_reclaim_needed()) { 4966 /* memory is low, delay before restarting */ 4967 ARCSTAT_INCR(arcstat_memory_throttle_count, 1); 4968 return (SET_ERROR(EAGAIN)); 4969 } 4970 page_load = 0; 4971#endif 4972 return (0); 4973} 4974 4975void 4976arc_tempreserve_clear(uint64_t reserve) 4977{ 4978 atomic_add_64(&arc_tempreserve, -reserve); 4979 ASSERT((int64_t)arc_tempreserve >= 0); 4980} 4981 4982int 4983arc_tempreserve_space(uint64_t reserve, uint64_t txg) 4984{ 4985 int error; 4986 uint64_t anon_size; 4987 4988 if (reserve > arc_c/4 && !arc_no_grow) { 4989 arc_c = MIN(arc_c_max, reserve * 4); 4990 DTRACE_PROBE1(arc__set_reserve, uint64_t, arc_c); 4991 } 4992 if (reserve > arc_c) 4993 return (SET_ERROR(ENOMEM)); 4994 4995 /* 4996 * Don't count loaned bufs as in flight dirty data to prevent long 4997 * network delays from blocking transactions that are ready to be 4998 * assigned to a txg. 4999 */ 5000 anon_size = MAX((int64_t)(arc_anon->arcs_size - arc_loaned_bytes), 0); 5001 5002 /* 5003 * Writes will, almost always, require additional memory allocations 5004 * in order to compress/encrypt/etc the data. We therefore need to 5005 * make sure that there is sufficient available memory for this. 5006 */ 5007 error = arc_memory_throttle(reserve, txg); 5008 if (error != 0) 5009 return (error); 5010 5011 /* 5012 * Throttle writes when the amount of dirty data in the cache 5013 * gets too large. We try to keep the cache less than half full 5014 * of dirty blocks so that our sync times don't grow too large. 5015 * Note: if two requests come in concurrently, we might let them 5016 * both succeed, when one of them should fail. Not a huge deal. 5017 */ 5018 5019 if (reserve + arc_tempreserve + anon_size > arc_c / 2 && 5020 anon_size > arc_c / 4) { 5021 dprintf("failing, arc_tempreserve=%lluK anon_meta=%lluK " 5022 "anon_data=%lluK tempreserve=%lluK arc_c=%lluK\n", 5023 arc_tempreserve>>10, 5024 arc_anon->arcs_lsize[ARC_BUFC_METADATA]>>10, 5025 arc_anon->arcs_lsize[ARC_BUFC_DATA]>>10, 5026 reserve>>10, arc_c>>10); 5027 return (SET_ERROR(ERESTART)); 5028 } 5029 atomic_add_64(&arc_tempreserve, reserve); 5030 return (0); 5031} 5032 5033static void 5034arc_kstat_update_state(arc_state_t *state, kstat_named_t *size, 5035 kstat_named_t *evict_data, kstat_named_t *evict_metadata) 5036{ 5037 size->value.ui64 = state->arcs_size; 5038 evict_data->value.ui64 = state->arcs_lsize[ARC_BUFC_DATA]; 5039 evict_metadata->value.ui64 = state->arcs_lsize[ARC_BUFC_METADATA]; 5040} 5041 5042static int 5043arc_kstat_update(kstat_t *ksp, int rw) 5044{ 5045 arc_stats_t *as = ksp->ks_data; 5046 5047 if (rw == KSTAT_WRITE) { 5048 return (EACCES); 5049 } else { 5050 arc_kstat_update_state(arc_anon, 5051 &as->arcstat_anon_size, 5052 &as->arcstat_anon_evictable_data, 5053 &as->arcstat_anon_evictable_metadata); 5054 arc_kstat_update_state(arc_mru, 5055 &as->arcstat_mru_size, 5056 &as->arcstat_mru_evictable_data, 5057 &as->arcstat_mru_evictable_metadata); 5058 arc_kstat_update_state(arc_mru_ghost, 5059 &as->arcstat_mru_ghost_size, 5060 &as->arcstat_mru_ghost_evictable_data, 5061 &as->arcstat_mru_ghost_evictable_metadata); 5062 arc_kstat_update_state(arc_mfu, 5063 &as->arcstat_mfu_size, 5064 &as->arcstat_mfu_evictable_data, 5065 &as->arcstat_mfu_evictable_metadata); 5066 arc_kstat_update_state(arc_mfu_ghost, 5067 &as->arcstat_mfu_ghost_size, 5068 &as->arcstat_mfu_ghost_evictable_data, 5069 &as->arcstat_mfu_ghost_evictable_metadata); 5070 } 5071 5072 return (0); 5073} 5074 5075/* 5076 * This function *must* return indices evenly distributed between all 5077 * sublists of the multilist. This is needed due to how the ARC eviction 5078 * code is laid out; arc_evict_state() assumes ARC buffers are evenly 5079 * distributed between all sublists and uses this assumption when 5080 * deciding which sublist to evict from and how much to evict from it. 5081 */ 5082unsigned int 5083arc_state_multilist_index_func(multilist_t *ml, void *obj) 5084{ 5085 arc_buf_hdr_t *hdr = obj; 5086 5087 /* 5088 * We rely on b_dva to generate evenly distributed index 5089 * numbers using buf_hash below. So, as an added precaution, 5090 * let's make sure we never add empty buffers to the arc lists. 5091 */ 5092 ASSERT(!BUF_EMPTY(hdr)); 5093 5094 /* 5095 * The assumption here, is the hash value for a given 5096 * arc_buf_hdr_t will remain constant throughout it's lifetime 5097 * (i.e. it's b_spa, b_dva, and b_birth fields don't change). 5098 * Thus, we don't need to store the header's sublist index 5099 * on insertion, as this index can be recalculated on removal. 5100 * 5101 * Also, the low order bits of the hash value are thought to be 5102 * distributed evenly. Otherwise, in the case that the multilist 5103 * has a power of two number of sublists, each sublists' usage 5104 * would not be evenly distributed. 5105 */ 5106 return (buf_hash(hdr->b_spa, &hdr->b_dva, hdr->b_birth) % 5107 multilist_get_num_sublists(ml)); 5108} 5109 5110#ifdef _KERNEL 5111static eventhandler_tag arc_event_lowmem = NULL; 5112 5113static void 5114arc_lowmem(void *arg __unused, int howto __unused) 5115{ 5116 5117 mutex_enter(&arc_reclaim_lock); 5118 /* XXX: Memory deficit should be passed as argument. */ 5119 needfree = btoc(arc_c >> arc_shrink_shift); 5120 DTRACE_PROBE(arc__needfree); 5121 cv_signal(&arc_reclaim_thread_cv); 5122 5123 /* 5124 * It is unsafe to block here in arbitrary threads, because we can come 5125 * here from ARC itself and may hold ARC locks and thus risk a deadlock 5126 * with ARC reclaim thread. 5127 */ 5128 if (curproc == pageproc) 5129 (void) cv_wait(&arc_reclaim_waiters_cv, &arc_reclaim_lock); 5130 mutex_exit(&arc_reclaim_lock); 5131} 5132#endif 5133 5134void 5135arc_init(void) 5136{ 5137 int i, prefetch_tunable_set = 0; 5138 5139 mutex_init(&arc_reclaim_lock, NULL, MUTEX_DEFAULT, NULL); 5140 cv_init(&arc_reclaim_thread_cv, NULL, CV_DEFAULT, NULL); 5141 cv_init(&arc_reclaim_waiters_cv, NULL, CV_DEFAULT, NULL); 5142 5143 mutex_init(&arc_user_evicts_lock, NULL, MUTEX_DEFAULT, NULL); 5144 cv_init(&arc_user_evicts_cv, NULL, CV_DEFAULT, NULL); 5145 5146 /* Convert seconds to clock ticks */ 5147 arc_min_prefetch_lifespan = 1 * hz; 5148 5149 /* Start out with 1/8 of all memory */ 5150 arc_c = kmem_size() / 8; 5151 5152#ifdef sun 5153#ifdef _KERNEL 5154 /* 5155 * On architectures where the physical memory can be larger 5156 * than the addressable space (intel in 32-bit mode), we may 5157 * need to limit the cache to 1/8 of VM size. 5158 */ 5159 arc_c = MIN(arc_c, vmem_size(heap_arena, VMEM_ALLOC | VMEM_FREE) / 8); 5160#endif 5161#endif /* sun */ 5162 /* set min cache to 1/32 of all memory, or 16MB, whichever is more */ 5163 arc_c_min = MAX(arc_c / 4, 16 << 20); 5164 /* set max to 1/2 of all memory, or all but 1GB, whichever is more */ 5165 if (arc_c * 8 >= 1 << 30) 5166 arc_c_max = (arc_c * 8) - (1 << 30); 5167 else 5168 arc_c_max = arc_c_min; 5169 arc_c_max = MAX(arc_c * 5, arc_c_max); 5170 5171#ifdef _KERNEL 5172 /* 5173 * Allow the tunables to override our calculations if they are 5174 * reasonable (ie. over 16MB) 5175 */ 5176 if (zfs_arc_max > 16 << 20 && zfs_arc_max < kmem_size()) 5177 arc_c_max = zfs_arc_max; 5178 if (zfs_arc_min > 16 << 20 && zfs_arc_min <= arc_c_max) 5179 arc_c_min = zfs_arc_min; 5180#endif 5181 5182 arc_c = arc_c_max; 5183 arc_p = (arc_c >> 1); 5184 5185 /* limit meta-data to 1/4 of the arc capacity */ 5186 arc_meta_limit = arc_c_max / 4; 5187 5188 /* Allow the tunable to override if it is reasonable */ 5189 if (zfs_arc_meta_limit > 0 && zfs_arc_meta_limit <= arc_c_max) 5190 arc_meta_limit = zfs_arc_meta_limit; 5191 5192 if (arc_c_min < arc_meta_limit / 2 && zfs_arc_min == 0) 5193 arc_c_min = arc_meta_limit / 2; 5194 5195 if (zfs_arc_meta_min > 0) { 5196 arc_meta_min = zfs_arc_meta_min; 5197 } else { 5198 arc_meta_min = arc_c_min / 2; 5199 } 5200 5201 if (zfs_arc_grow_retry > 0) 5202 arc_grow_retry = zfs_arc_grow_retry; 5203 5204 if (zfs_arc_shrink_shift > 0) 5205 arc_shrink_shift = zfs_arc_shrink_shift; 5206 5207 /* 5208 * Ensure that arc_no_grow_shift is less than arc_shrink_shift. 5209 */ 5210 if (arc_no_grow_shift >= arc_shrink_shift) 5211 arc_no_grow_shift = arc_shrink_shift - 1; 5212 5213 if (zfs_arc_p_min_shift > 0) 5214 arc_p_min_shift = zfs_arc_p_min_shift; 5215 5216 if (zfs_arc_num_sublists_per_state < 1) 5217 zfs_arc_num_sublists_per_state = MAX(max_ncpus, 1); 5218 5219 /* if kmem_flags are set, lets try to use less memory */ 5220 if (kmem_debugging()) 5221 arc_c = arc_c / 2; 5222 if (arc_c < arc_c_min) 5223 arc_c = arc_c_min; 5224 5225 zfs_arc_min = arc_c_min; 5226 zfs_arc_max = arc_c_max; 5227 5228 arc_anon = &ARC_anon; 5229 arc_mru = &ARC_mru; 5230 arc_mru_ghost = &ARC_mru_ghost; 5231 arc_mfu = &ARC_mfu; 5232 arc_mfu_ghost = &ARC_mfu_ghost; 5233 arc_l2c_only = &ARC_l2c_only; 5234 arc_size = 0; 5235 5236 multilist_create(&arc_mru->arcs_list[ARC_BUFC_METADATA], 5237 sizeof (arc_buf_hdr_t), 5238 offsetof(arc_buf_hdr_t, b_l1hdr.b_arc_node), 5239 zfs_arc_num_sublists_per_state, arc_state_multilist_index_func); 5240 multilist_create(&arc_mru->arcs_list[ARC_BUFC_DATA], 5241 sizeof (arc_buf_hdr_t), 5242 offsetof(arc_buf_hdr_t, b_l1hdr.b_arc_node), 5243 zfs_arc_num_sublists_per_state, arc_state_multilist_index_func); 5244 multilist_create(&arc_mru_ghost->arcs_list[ARC_BUFC_METADATA], 5245 sizeof (arc_buf_hdr_t), 5246 offsetof(arc_buf_hdr_t, b_l1hdr.b_arc_node), 5247 zfs_arc_num_sublists_per_state, arc_state_multilist_index_func); 5248 multilist_create(&arc_mru_ghost->arcs_list[ARC_BUFC_DATA], 5249 sizeof (arc_buf_hdr_t), 5250 offsetof(arc_buf_hdr_t, b_l1hdr.b_arc_node), 5251 zfs_arc_num_sublists_per_state, arc_state_multilist_index_func); 5252 multilist_create(&arc_mfu->arcs_list[ARC_BUFC_METADATA], 5253 sizeof (arc_buf_hdr_t), 5254 offsetof(arc_buf_hdr_t, b_l1hdr.b_arc_node), 5255 zfs_arc_num_sublists_per_state, arc_state_multilist_index_func); 5256 multilist_create(&arc_mfu->arcs_list[ARC_BUFC_DATA], 5257 sizeof (arc_buf_hdr_t), 5258 offsetof(arc_buf_hdr_t, b_l1hdr.b_arc_node), 5259 zfs_arc_num_sublists_per_state, arc_state_multilist_index_func); 5260 multilist_create(&arc_mfu_ghost->arcs_list[ARC_BUFC_METADATA], 5261 sizeof (arc_buf_hdr_t), 5262 offsetof(arc_buf_hdr_t, b_l1hdr.b_arc_node), 5263 zfs_arc_num_sublists_per_state, arc_state_multilist_index_func); 5264 multilist_create(&arc_mfu_ghost->arcs_list[ARC_BUFC_DATA], 5265 sizeof (arc_buf_hdr_t), 5266 offsetof(arc_buf_hdr_t, b_l1hdr.b_arc_node), 5267 zfs_arc_num_sublists_per_state, arc_state_multilist_index_func); 5268 multilist_create(&arc_l2c_only->arcs_list[ARC_BUFC_METADATA], 5269 sizeof (arc_buf_hdr_t), 5270 offsetof(arc_buf_hdr_t, b_l1hdr.b_arc_node), 5271 zfs_arc_num_sublists_per_state, arc_state_multilist_index_func); 5272 multilist_create(&arc_l2c_only->arcs_list[ARC_BUFC_DATA], 5273 sizeof (arc_buf_hdr_t), 5274 offsetof(arc_buf_hdr_t, b_l1hdr.b_arc_node), 5275 zfs_arc_num_sublists_per_state, arc_state_multilist_index_func); 5276 5277 buf_init(); 5278 5279 arc_reclaim_thread_exit = FALSE; 5280 arc_user_evicts_thread_exit = FALSE; 5281 arc_eviction_list = NULL; 5282 bzero(&arc_eviction_hdr, sizeof (arc_buf_hdr_t)); 5283 5284 arc_ksp = kstat_create("zfs", 0, "arcstats", "misc", KSTAT_TYPE_NAMED, 5285 sizeof (arc_stats) / sizeof (kstat_named_t), KSTAT_FLAG_VIRTUAL); 5286 5287 if (arc_ksp != NULL) { 5288 arc_ksp->ks_data = &arc_stats; 5289 arc_ksp->ks_update = arc_kstat_update; 5290 kstat_install(arc_ksp); 5291 } 5292 5293 (void) thread_create(NULL, 0, arc_reclaim_thread, NULL, 0, &p0, 5294 TS_RUN, minclsyspri); 5295 5296#ifdef _KERNEL 5297 arc_event_lowmem = EVENTHANDLER_REGISTER(vm_lowmem, arc_lowmem, NULL, 5298 EVENTHANDLER_PRI_FIRST); 5299#endif 5300 5301 (void) thread_create(NULL, 0, arc_user_evicts_thread, NULL, 0, &p0, 5302 TS_RUN, minclsyspri); 5303 5304 arc_dead = FALSE; 5305 arc_warm = B_FALSE; 5306 5307 /* 5308 * Calculate maximum amount of dirty data per pool. 5309 * 5310 * If it has been set by /etc/system, take that. 5311 * Otherwise, use a percentage of physical memory defined by 5312 * zfs_dirty_data_max_percent (default 10%) with a cap at 5313 * zfs_dirty_data_max_max (default 4GB). 5314 */ 5315 if (zfs_dirty_data_max == 0) { 5316 zfs_dirty_data_max = ptob(physmem) * 5317 zfs_dirty_data_max_percent / 100; 5318 zfs_dirty_data_max = MIN(zfs_dirty_data_max, 5319 zfs_dirty_data_max_max); 5320 } 5321 5322#ifdef _KERNEL 5323 if (TUNABLE_INT_FETCH("vfs.zfs.prefetch_disable", &zfs_prefetch_disable)) 5324 prefetch_tunable_set = 1; 5325 5326#ifdef __i386__ 5327 if (prefetch_tunable_set == 0) { 5328 printf("ZFS NOTICE: Prefetch is disabled by default on i386 " 5329 "-- to enable,\n"); 5330 printf(" add \"vfs.zfs.prefetch_disable=0\" " 5331 "to /boot/loader.conf.\n"); 5332 zfs_prefetch_disable = 1; 5333 } 5334#else 5335 if ((((uint64_t)physmem * PAGESIZE) < (1ULL << 32)) && 5336 prefetch_tunable_set == 0) { 5337 printf("ZFS NOTICE: Prefetch is disabled by default if less " 5338 "than 4GB of RAM is present;\n" 5339 " to enable, add \"vfs.zfs.prefetch_disable=0\" " 5340 "to /boot/loader.conf.\n"); 5341 zfs_prefetch_disable = 1; 5342 } 5343#endif 5344 /* Warn about ZFS memory and address space requirements. */ 5345 if (((uint64_t)physmem * PAGESIZE) < (256 + 128 + 64) * (1 << 20)) { 5346 printf("ZFS WARNING: Recommended minimum RAM size is 512MB; " 5347 "expect unstable behavior.\n"); 5348 } 5349 if (kmem_size() < 512 * (1 << 20)) { 5350 printf("ZFS WARNING: Recommended minimum kmem_size is 512MB; " 5351 "expect unstable behavior.\n"); 5352 printf(" Consider tuning vm.kmem_size and " 5353 "vm.kmem_size_max\n"); 5354 printf(" in /boot/loader.conf.\n"); 5355 } 5356#endif 5357} 5358 5359void 5360arc_fini(void) 5361{ 5362 mutex_enter(&arc_reclaim_lock); 5363 arc_reclaim_thread_exit = TRUE; 5364 /* 5365 * The reclaim thread will set arc_reclaim_thread_exit back to 5366 * FALSE when it is finished exiting; we're waiting for that. 5367 */ 5368 while (arc_reclaim_thread_exit) { 5369 cv_signal(&arc_reclaim_thread_cv); 5370 cv_wait(&arc_reclaim_thread_cv, &arc_reclaim_lock); 5371 } 5372 mutex_exit(&arc_reclaim_lock); 5373 5374 mutex_enter(&arc_user_evicts_lock); 5375 arc_user_evicts_thread_exit = TRUE; 5376 /* 5377 * The user evicts thread will set arc_user_evicts_thread_exit 5378 * to FALSE when it is finished exiting; we're waiting for that. 5379 */ 5380 while (arc_user_evicts_thread_exit) { 5381 cv_signal(&arc_user_evicts_cv); 5382 cv_wait(&arc_user_evicts_cv, &arc_user_evicts_lock); 5383 } 5384 mutex_exit(&arc_user_evicts_lock); 5385 5386 /* Use TRUE to ensure *all* buffers are evicted */ 5387 arc_flush(NULL, TRUE); 5388 5389 arc_dead = TRUE; 5390 5391 if (arc_ksp != NULL) { 5392 kstat_delete(arc_ksp); 5393 arc_ksp = NULL; 5394 } 5395 5396 mutex_destroy(&arc_reclaim_lock); 5397 cv_destroy(&arc_reclaim_thread_cv); 5398 cv_destroy(&arc_reclaim_waiters_cv); 5399 5400 mutex_destroy(&arc_user_evicts_lock); 5401 cv_destroy(&arc_user_evicts_cv); 5402 5403 multilist_destroy(&arc_mru->arcs_list[ARC_BUFC_METADATA]); 5404 multilist_destroy(&arc_mru_ghost->arcs_list[ARC_BUFC_METADATA]); 5405 multilist_destroy(&arc_mfu->arcs_list[ARC_BUFC_METADATA]); 5406 multilist_destroy(&arc_mfu_ghost->arcs_list[ARC_BUFC_METADATA]); 5407 multilist_destroy(&arc_mru->arcs_list[ARC_BUFC_DATA]); 5408 multilist_destroy(&arc_mru_ghost->arcs_list[ARC_BUFC_DATA]); 5409 multilist_destroy(&arc_mfu->arcs_list[ARC_BUFC_DATA]); 5410 multilist_destroy(&arc_mfu_ghost->arcs_list[ARC_BUFC_DATA]); 5411 5412 buf_fini(); 5413 5414 ASSERT0(arc_loaned_bytes); 5415 5416#ifdef _KERNEL 5417 if (arc_event_lowmem != NULL) 5418 EVENTHANDLER_DEREGISTER(vm_lowmem, arc_event_lowmem); 5419#endif 5420} 5421 5422/* 5423 * Level 2 ARC 5424 * 5425 * The level 2 ARC (L2ARC) is a cache layer in-between main memory and disk. 5426 * It uses dedicated storage devices to hold cached data, which are populated 5427 * using large infrequent writes. The main role of this cache is to boost 5428 * the performance of random read workloads. The intended L2ARC devices 5429 * include short-stroked disks, solid state disks, and other media with 5430 * substantially faster read latency than disk. 5431 * 5432 * +-----------------------+ 5433 * | ARC | 5434 * +-----------------------+ 5435 * | ^ ^ 5436 * | | | 5437 * l2arc_feed_thread() arc_read() 5438 * | | | 5439 * | l2arc read | 5440 * V | | 5441 * +---------------+ | 5442 * | L2ARC | | 5443 * +---------------+ | 5444 * | ^ | 5445 * l2arc_write() | | 5446 * | | | 5447 * V | | 5448 * +-------+ +-------+ 5449 * | vdev | | vdev | 5450 * | cache | | cache | 5451 * +-------+ +-------+ 5452 * +=========+ .-----. 5453 * : L2ARC : |-_____-| 5454 * : devices : | Disks | 5455 * +=========+ `-_____-' 5456 * 5457 * Read requests are satisfied from the following sources, in order: 5458 * 5459 * 1) ARC 5460 * 2) vdev cache of L2ARC devices 5461 * 3) L2ARC devices 5462 * 4) vdev cache of disks 5463 * 5) disks 5464 * 5465 * Some L2ARC device types exhibit extremely slow write performance. 5466 * To accommodate for this there are some significant differences between 5467 * the L2ARC and traditional cache design: 5468 * 5469 * 1. There is no eviction path from the ARC to the L2ARC. Evictions from 5470 * the ARC behave as usual, freeing buffers and placing headers on ghost 5471 * lists. The ARC does not send buffers to the L2ARC during eviction as 5472 * this would add inflated write latencies for all ARC memory pressure. 5473 * 5474 * 2. The L2ARC attempts to cache data from the ARC before it is evicted. 5475 * It does this by periodically scanning buffers from the eviction-end of 5476 * the MFU and MRU ARC lists, copying them to the L2ARC devices if they are 5477 * not already there. It scans until a headroom of buffers is satisfied, 5478 * which itself is a buffer for ARC eviction. If a compressible buffer is 5479 * found during scanning and selected for writing to an L2ARC device, we 5480 * temporarily boost scanning headroom during the next scan cycle to make 5481 * sure we adapt to compression effects (which might significantly reduce 5482 * the data volume we write to L2ARC). The thread that does this is 5483 * l2arc_feed_thread(), illustrated below; example sizes are included to 5484 * provide a better sense of ratio than this diagram: 5485 * 5486 * head --> tail 5487 * +---------------------+----------+ 5488 * ARC_mfu |:::::#:::::::::::::::|o#o###o###|-->. # already on L2ARC 5489 * +---------------------+----------+ | o L2ARC eligible 5490 * ARC_mru |:#:::::::::::::::::::|#o#ooo####|-->| : ARC buffer 5491 * +---------------------+----------+ | 5492 * 15.9 Gbytes ^ 32 Mbytes | 5493 * headroom | 5494 * l2arc_feed_thread() 5495 * | 5496 * l2arc write hand <--[oooo]--' 5497 * | 8 Mbyte 5498 * | write max 5499 * V 5500 * +==============================+ 5501 * L2ARC dev |####|#|###|###| |####| ... | 5502 * +==============================+ 5503 * 32 Gbytes 5504 * 5505 * 3. If an ARC buffer is copied to the L2ARC but then hit instead of 5506 * evicted, then the L2ARC has cached a buffer much sooner than it probably 5507 * needed to, potentially wasting L2ARC device bandwidth and storage. It is 5508 * safe to say that this is an uncommon case, since buffers at the end of 5509 * the ARC lists have moved there due to inactivity. 5510 * 5511 * 4. If the ARC evicts faster than the L2ARC can maintain a headroom, 5512 * then the L2ARC simply misses copying some buffers. This serves as a 5513 * pressure valve to prevent heavy read workloads from both stalling the ARC 5514 * with waits and clogging the L2ARC with writes. This also helps prevent 5515 * the potential for the L2ARC to churn if it attempts to cache content too 5516 * quickly, such as during backups of the entire pool. 5517 * 5518 * 5. After system boot and before the ARC has filled main memory, there are 5519 * no evictions from the ARC and so the tails of the ARC_mfu and ARC_mru 5520 * lists can remain mostly static. Instead of searching from tail of these 5521 * lists as pictured, the l2arc_feed_thread() will search from the list heads 5522 * for eligible buffers, greatly increasing its chance of finding them. 5523 * 5524 * The L2ARC device write speed is also boosted during this time so that 5525 * the L2ARC warms up faster. Since there have been no ARC evictions yet, 5526 * there are no L2ARC reads, and no fear of degrading read performance 5527 * through increased writes. 5528 * 5529 * 6. Writes to the L2ARC devices are grouped and sent in-sequence, so that 5530 * the vdev queue can aggregate them into larger and fewer writes. Each 5531 * device is written to in a rotor fashion, sweeping writes through 5532 * available space then repeating. 5533 * 5534 * 7. The L2ARC does not store dirty content. It never needs to flush 5535 * write buffers back to disk based storage. 5536 * 5537 * 8. If an ARC buffer is written (and dirtied) which also exists in the 5538 * L2ARC, the now stale L2ARC buffer is immediately dropped. 5539 * 5540 * The performance of the L2ARC can be tweaked by a number of tunables, which 5541 * may be necessary for different workloads: 5542 * 5543 * l2arc_write_max max write bytes per interval 5544 * l2arc_write_boost extra write bytes during device warmup 5545 * l2arc_noprefetch skip caching prefetched buffers 5546 * l2arc_headroom number of max device writes to precache 5547 * l2arc_headroom_boost when we find compressed buffers during ARC 5548 * scanning, we multiply headroom by this 5549 * percentage factor for the next scan cycle, 5550 * since more compressed buffers are likely to 5551 * be present 5552 * l2arc_feed_secs seconds between L2ARC writing 5553 * 5554 * Tunables may be removed or added as future performance improvements are 5555 * integrated, and also may become zpool properties. 5556 * 5557 * There are three key functions that control how the L2ARC warms up: 5558 * 5559 * l2arc_write_eligible() check if a buffer is eligible to cache 5560 * l2arc_write_size() calculate how much to write 5561 * l2arc_write_interval() calculate sleep delay between writes 5562 * 5563 * These three functions determine what to write, how much, and how quickly 5564 * to send writes. 5565 */ 5566 5567static boolean_t 5568l2arc_write_eligible(uint64_t spa_guid, arc_buf_hdr_t *hdr) 5569{ 5570 /* 5571 * A buffer is *not* eligible for the L2ARC if it: 5572 * 1. belongs to a different spa. 5573 * 2. is already cached on the L2ARC. 5574 * 3. has an I/O in progress (it may be an incomplete read). 5575 * 4. is flagged not eligible (zfs property). 5576 */ 5577 if (hdr->b_spa != spa_guid) { 5578 ARCSTAT_BUMP(arcstat_l2_write_spa_mismatch); 5579 return (B_FALSE); 5580 } 5581 if (HDR_HAS_L2HDR(hdr)) { 5582 ARCSTAT_BUMP(arcstat_l2_write_in_l2); 5583 return (B_FALSE); 5584 } 5585 if (HDR_IO_IN_PROGRESS(hdr)) { 5586 ARCSTAT_BUMP(arcstat_l2_write_hdr_io_in_progress); 5587 return (B_FALSE); 5588 } 5589 if (!HDR_L2CACHE(hdr)) { 5590 ARCSTAT_BUMP(arcstat_l2_write_not_cacheable); 5591 return (B_FALSE); 5592 } 5593 5594 return (B_TRUE); 5595} 5596 5597static uint64_t 5598l2arc_write_size(void) 5599{ 5600 uint64_t size; 5601 5602 /* 5603 * Make sure our globals have meaningful values in case the user 5604 * altered them. 5605 */ 5606 size = l2arc_write_max; 5607 if (size == 0) { 5608 cmn_err(CE_NOTE, "Bad value for l2arc_write_max, value must " 5609 "be greater than zero, resetting it to the default (%d)", 5610 L2ARC_WRITE_SIZE); 5611 size = l2arc_write_max = L2ARC_WRITE_SIZE; 5612 } 5613 5614 if (arc_warm == B_FALSE) 5615 size += l2arc_write_boost; 5616 5617 return (size); 5618 5619} 5620 5621static clock_t 5622l2arc_write_interval(clock_t began, uint64_t wanted, uint64_t wrote) 5623{ 5624 clock_t interval, next, now; 5625 5626 /* 5627 * If the ARC lists are busy, increase our write rate; if the 5628 * lists are stale, idle back. This is achieved by checking 5629 * how much we previously wrote - if it was more than half of 5630 * what we wanted, schedule the next write much sooner. 5631 */ 5632 if (l2arc_feed_again && wrote > (wanted / 2)) 5633 interval = (hz * l2arc_feed_min_ms) / 1000; 5634 else 5635 interval = hz * l2arc_feed_secs; 5636 5637 now = ddi_get_lbolt(); 5638 next = MAX(now, MIN(now + interval, began + interval)); 5639 5640 return (next); 5641} 5642 5643/* 5644 * Cycle through L2ARC devices. This is how L2ARC load balances. 5645 * If a device is returned, this also returns holding the spa config lock. 5646 */ 5647static l2arc_dev_t * 5648l2arc_dev_get_next(void) 5649{ 5650 l2arc_dev_t *first, *next = NULL; 5651 5652 /* 5653 * Lock out the removal of spas (spa_namespace_lock), then removal 5654 * of cache devices (l2arc_dev_mtx). Once a device has been selected, 5655 * both locks will be dropped and a spa config lock held instead. 5656 */ 5657 mutex_enter(&spa_namespace_lock); 5658 mutex_enter(&l2arc_dev_mtx); 5659 5660 /* if there are no vdevs, there is nothing to do */ 5661 if (l2arc_ndev == 0) 5662 goto out; 5663 5664 first = NULL; 5665 next = l2arc_dev_last; 5666 do { 5667 /* loop around the list looking for a non-faulted vdev */ 5668 if (next == NULL) { 5669 next = list_head(l2arc_dev_list); 5670 } else { 5671 next = list_next(l2arc_dev_list, next); 5672 if (next == NULL) 5673 next = list_head(l2arc_dev_list); 5674 } 5675 5676 /* if we have come back to the start, bail out */ 5677 if (first == NULL) 5678 first = next; 5679 else if (next == first) 5680 break; 5681 5682 } while (vdev_is_dead(next->l2ad_vdev)); 5683 5684 /* if we were unable to find any usable vdevs, return NULL */ 5685 if (vdev_is_dead(next->l2ad_vdev)) 5686 next = NULL; 5687 5688 l2arc_dev_last = next; 5689 5690out: 5691 mutex_exit(&l2arc_dev_mtx); 5692 5693 /* 5694 * Grab the config lock to prevent the 'next' device from being 5695 * removed while we are writing to it. 5696 */ 5697 if (next != NULL) 5698 spa_config_enter(next->l2ad_spa, SCL_L2ARC, next, RW_READER); 5699 mutex_exit(&spa_namespace_lock); 5700 5701 return (next); 5702} 5703 5704/* 5705 * Free buffers that were tagged for destruction. 5706 */ 5707static void 5708l2arc_do_free_on_write() 5709{ 5710 list_t *buflist; 5711 l2arc_data_free_t *df, *df_prev; 5712 5713 mutex_enter(&l2arc_free_on_write_mtx); 5714 buflist = l2arc_free_on_write; 5715 5716 for (df = list_tail(buflist); df; df = df_prev) { 5717 df_prev = list_prev(buflist, df); 5718 ASSERT(df->l2df_data != NULL); 5719 ASSERT(df->l2df_func != NULL); 5720 df->l2df_func(df->l2df_data, df->l2df_size); 5721 list_remove(buflist, df); 5722 kmem_free(df, sizeof (l2arc_data_free_t)); 5723 } 5724 5725 mutex_exit(&l2arc_free_on_write_mtx); 5726} 5727 5728/* 5729 * A write to a cache device has completed. Update all headers to allow 5730 * reads from these buffers to begin. 5731 */ 5732static void 5733l2arc_write_done(zio_t *zio) 5734{ 5735 l2arc_write_callback_t *cb; 5736 l2arc_dev_t *dev; 5737 list_t *buflist; 5738 arc_buf_hdr_t *head, *hdr, *hdr_prev; 5739 kmutex_t *hash_lock; 5740 int64_t bytes_dropped = 0; 5741 5742 cb = zio->io_private; 5743 ASSERT(cb != NULL); 5744 dev = cb->l2wcb_dev; 5745 ASSERT(dev != NULL); 5746 head = cb->l2wcb_head; 5747 ASSERT(head != NULL); 5748 buflist = &dev->l2ad_buflist; 5749 ASSERT(buflist != NULL); 5750 DTRACE_PROBE2(l2arc__iodone, zio_t *, zio, 5751 l2arc_write_callback_t *, cb); 5752 5753 if (zio->io_error != 0) 5754 ARCSTAT_BUMP(arcstat_l2_writes_error); 5755 5756 /* 5757 * All writes completed, or an error was hit. 5758 */ 5759top: 5760 mutex_enter(&dev->l2ad_mtx); 5761 for (hdr = list_prev(buflist, head); hdr; hdr = hdr_prev) { 5762 hdr_prev = list_prev(buflist, hdr); 5763 5764 hash_lock = HDR_LOCK(hdr); 5765 5766 /* 5767 * We cannot use mutex_enter or else we can deadlock 5768 * with l2arc_write_buffers (due to swapping the order 5769 * the hash lock and l2ad_mtx are taken). 5770 */ 5771 if (!mutex_tryenter(hash_lock)) { 5772 /* 5773 * Missed the hash lock. We must retry so we 5774 * don't leave the ARC_FLAG_L2_WRITING bit set. 5775 */ 5776 ARCSTAT_BUMP(arcstat_l2_writes_lock_retry); 5777 5778 /* 5779 * We don't want to rescan the headers we've 5780 * already marked as having been written out, so 5781 * we reinsert the head node so we can pick up 5782 * where we left off. 5783 */ 5784 list_remove(buflist, head); 5785 list_insert_after(buflist, hdr, head); 5786 5787 mutex_exit(&dev->l2ad_mtx); 5788 5789 /* 5790 * We wait for the hash lock to become available 5791 * to try and prevent busy waiting, and increase 5792 * the chance we'll be able to acquire the lock 5793 * the next time around. 5794 */ 5795 mutex_enter(hash_lock); 5796 mutex_exit(hash_lock); 5797 goto top; 5798 } 5799 5800 /* 5801 * We could not have been moved into the arc_l2c_only 5802 * state while in-flight due to our ARC_FLAG_L2_WRITING 5803 * bit being set. Let's just ensure that's being enforced. 5804 */ 5805 ASSERT(HDR_HAS_L1HDR(hdr)); 5806 5807 /* 5808 * We may have allocated a buffer for L2ARC compression, 5809 * we must release it to avoid leaking this data. 5810 */ 5811 l2arc_release_cdata_buf(hdr); 5812 5813 if (zio->io_error != 0) { 5814 /* 5815 * Error - drop L2ARC entry. 5816 */ 5817 trim_map_free(hdr->b_l2hdr.b_dev->l2ad_vdev, 5818 hdr->b_l2hdr.b_daddr, hdr->b_l2hdr.b_asize, 0); 5819 hdr->b_flags &= ~ARC_FLAG_HAS_L2HDR; 5820 5821 ARCSTAT_INCR(arcstat_l2_asize, -hdr->b_l2hdr.b_asize); 5822 ARCSTAT_INCR(arcstat_l2_size, -hdr->b_size); 5823 5824 bytes_dropped += hdr->b_l2hdr.b_asize; 5825 (void) refcount_remove_many(&dev->l2ad_alloc, 5826 hdr->b_l2hdr.b_asize, hdr); 5827 } 5828 5829 /* 5830 * Allow ARC to begin reads and ghost list evictions to 5831 * this L2ARC entry. 5832 */ 5833 hdr->b_flags &= ~ARC_FLAG_L2_WRITING; 5834 5835 mutex_exit(hash_lock); 5836 } 5837 5838 atomic_inc_64(&l2arc_writes_done); 5839 list_remove(buflist, head); 5840 ASSERT(!HDR_HAS_L1HDR(head)); 5841 kmem_cache_free(hdr_l2only_cache, head); 5842 mutex_exit(&dev->l2ad_mtx); 5843 5844 vdev_space_update(dev->l2ad_vdev, -bytes_dropped, 0, 0); 5845 5846 l2arc_do_free_on_write(); 5847 5848 kmem_free(cb, sizeof (l2arc_write_callback_t)); 5849} 5850 5851/* 5852 * A read to a cache device completed. Validate buffer contents before 5853 * handing over to the regular ARC routines. 5854 */ 5855static void 5856l2arc_read_done(zio_t *zio) 5857{ 5858 l2arc_read_callback_t *cb; 5859 arc_buf_hdr_t *hdr; 5860 arc_buf_t *buf; 5861 kmutex_t *hash_lock; 5862 int equal; 5863 5864 ASSERT(zio->io_vd != NULL); 5865 ASSERT(zio->io_flags & ZIO_FLAG_DONT_PROPAGATE); 5866 5867 spa_config_exit(zio->io_spa, SCL_L2ARC, zio->io_vd); 5868 5869 cb = zio->io_private; 5870 ASSERT(cb != NULL); 5871 buf = cb->l2rcb_buf; 5872 ASSERT(buf != NULL); 5873 5874 hash_lock = HDR_LOCK(buf->b_hdr); 5875 mutex_enter(hash_lock); 5876 hdr = buf->b_hdr; 5877 ASSERT3P(hash_lock, ==, HDR_LOCK(hdr)); 5878 5879 /* 5880 * If the buffer was compressed, decompress it first. 5881 */ 5882 if (cb->l2rcb_compress != ZIO_COMPRESS_OFF) 5883 l2arc_decompress_zio(zio, hdr, cb->l2rcb_compress); 5884 ASSERT(zio->io_data != NULL); 5885 5886 /* 5887 * Check this survived the L2ARC journey. 5888 */ 5889 equal = arc_cksum_equal(buf); 5890 if (equal && zio->io_error == 0 && !HDR_L2_EVICTED(hdr)) { 5891 mutex_exit(hash_lock); 5892 zio->io_private = buf; 5893 zio->io_bp_copy = cb->l2rcb_bp; /* XXX fix in L2ARC 2.0 */ 5894 zio->io_bp = &zio->io_bp_copy; /* XXX fix in L2ARC 2.0 */ 5895 arc_read_done(zio); 5896 } else { 5897 mutex_exit(hash_lock); 5898 /* 5899 * Buffer didn't survive caching. Increment stats and 5900 * reissue to the original storage device. 5901 */ 5902 if (zio->io_error != 0) { 5903 ARCSTAT_BUMP(arcstat_l2_io_error); 5904 } else { 5905 zio->io_error = SET_ERROR(EIO); 5906 } 5907 if (!equal) 5908 ARCSTAT_BUMP(arcstat_l2_cksum_bad); 5909 5910 /* 5911 * If there's no waiter, issue an async i/o to the primary 5912 * storage now. If there *is* a waiter, the caller must 5913 * issue the i/o in a context where it's OK to block. 5914 */ 5915 if (zio->io_waiter == NULL) { 5916 zio_t *pio = zio_unique_parent(zio); 5917 5918 ASSERT(!pio || pio->io_child_type == ZIO_CHILD_LOGICAL); 5919 5920 zio_nowait(zio_read(pio, cb->l2rcb_spa, &cb->l2rcb_bp, 5921 buf->b_data, zio->io_size, arc_read_done, buf, 5922 zio->io_priority, cb->l2rcb_flags, &cb->l2rcb_zb)); 5923 } 5924 } 5925 5926 kmem_free(cb, sizeof (l2arc_read_callback_t)); 5927} 5928 5929/* 5930 * This is the list priority from which the L2ARC will search for pages to 5931 * cache. This is used within loops (0..3) to cycle through lists in the 5932 * desired order. This order can have a significant effect on cache 5933 * performance. 5934 * 5935 * Currently the metadata lists are hit first, MFU then MRU, followed by 5936 * the data lists. This function returns a locked list, and also returns 5937 * the lock pointer. 5938 */ 5939static multilist_sublist_t * 5940l2arc_sublist_lock(int list_num) 5941{ 5942 multilist_t *ml = NULL; 5943 unsigned int idx; 5944 5945 ASSERT(list_num >= 0 && list_num <= 3); 5946 5947 switch (list_num) { 5948 case 0: 5949 ml = &arc_mfu->arcs_list[ARC_BUFC_METADATA]; 5950 break; 5951 case 1: 5952 ml = &arc_mru->arcs_list[ARC_BUFC_METADATA]; 5953 break; 5954 case 2: 5955 ml = &arc_mfu->arcs_list[ARC_BUFC_DATA]; 5956 break; 5957 case 3: 5958 ml = &arc_mru->arcs_list[ARC_BUFC_DATA]; 5959 break; 5960 } 5961 5962 /* 5963 * Return a randomly-selected sublist. This is acceptable 5964 * because the caller feeds only a little bit of data for each 5965 * call (8MB). Subsequent calls will result in different 5966 * sublists being selected. 5967 */ 5968 idx = multilist_get_random_index(ml); 5969 return (multilist_sublist_lock(ml, idx)); 5970} 5971 5972/* 5973 * Evict buffers from the device write hand to the distance specified in 5974 * bytes. This distance may span populated buffers, it may span nothing. 5975 * This is clearing a region on the L2ARC device ready for writing. 5976 * If the 'all' boolean is set, every buffer is evicted. 5977 */ 5978static void 5979l2arc_evict(l2arc_dev_t *dev, uint64_t distance, boolean_t all) 5980{ 5981 list_t *buflist; 5982 arc_buf_hdr_t *hdr, *hdr_prev; 5983 kmutex_t *hash_lock; 5984 uint64_t taddr; 5985 5986 buflist = &dev->l2ad_buflist; 5987 5988 if (!all && dev->l2ad_first) { 5989 /* 5990 * This is the first sweep through the device. There is 5991 * nothing to evict. 5992 */ 5993 return; 5994 } 5995 5996 if (dev->l2ad_hand >= (dev->l2ad_end - (2 * distance))) { 5997 /* 5998 * When nearing the end of the device, evict to the end 5999 * before the device write hand jumps to the start. 6000 */ 6001 taddr = dev->l2ad_end; 6002 } else { 6003 taddr = dev->l2ad_hand + distance; 6004 } 6005 DTRACE_PROBE4(l2arc__evict, l2arc_dev_t *, dev, list_t *, buflist, 6006 uint64_t, taddr, boolean_t, all); 6007 6008top: 6009 mutex_enter(&dev->l2ad_mtx); 6010 for (hdr = list_tail(buflist); hdr; hdr = hdr_prev) { 6011 hdr_prev = list_prev(buflist, hdr); 6012 6013 hash_lock = HDR_LOCK(hdr); 6014 6015 /* 6016 * We cannot use mutex_enter or else we can deadlock 6017 * with l2arc_write_buffers (due to swapping the order 6018 * the hash lock and l2ad_mtx are taken). 6019 */ 6020 if (!mutex_tryenter(hash_lock)) { 6021 /* 6022 * Missed the hash lock. Retry. 6023 */ 6024 ARCSTAT_BUMP(arcstat_l2_evict_lock_retry); 6025 mutex_exit(&dev->l2ad_mtx); 6026 mutex_enter(hash_lock); 6027 mutex_exit(hash_lock); 6028 goto top; 6029 } 6030 6031 if (HDR_L2_WRITE_HEAD(hdr)) { 6032 /* 6033 * We hit a write head node. Leave it for 6034 * l2arc_write_done(). 6035 */ 6036 list_remove(buflist, hdr); 6037 mutex_exit(hash_lock); 6038 continue; 6039 } 6040 6041 if (!all && HDR_HAS_L2HDR(hdr) && 6042 (hdr->b_l2hdr.b_daddr > taddr || 6043 hdr->b_l2hdr.b_daddr < dev->l2ad_hand)) { 6044 /* 6045 * We've evicted to the target address, 6046 * or the end of the device. 6047 */ 6048 mutex_exit(hash_lock); 6049 break; 6050 } 6051 6052 ASSERT(HDR_HAS_L2HDR(hdr)); 6053 if (!HDR_HAS_L1HDR(hdr)) { 6054 ASSERT(!HDR_L2_READING(hdr)); 6055 /* 6056 * This doesn't exist in the ARC. Destroy. 6057 * arc_hdr_destroy() will call list_remove() 6058 * and decrement arcstat_l2_size. 6059 */ 6060 arc_change_state(arc_anon, hdr, hash_lock); 6061 arc_hdr_destroy(hdr); 6062 } else { 6063 ASSERT(hdr->b_l1hdr.b_state != arc_l2c_only); 6064 ARCSTAT_BUMP(arcstat_l2_evict_l1cached); 6065 /* 6066 * Invalidate issued or about to be issued 6067 * reads, since we may be about to write 6068 * over this location. 6069 */ 6070 if (HDR_L2_READING(hdr)) { 6071 ARCSTAT_BUMP(arcstat_l2_evict_reading); 6072 hdr->b_flags |= ARC_FLAG_L2_EVICTED; 6073 } 6074 6075 /* Ensure this header has finished being written */ 6076 ASSERT(!HDR_L2_WRITING(hdr)); 6077 ASSERT3P(hdr->b_l1hdr.b_tmp_cdata, ==, NULL); 6078 6079 arc_hdr_l2hdr_destroy(hdr); 6080 } 6081 mutex_exit(hash_lock); 6082 } 6083 mutex_exit(&dev->l2ad_mtx); 6084} 6085 6086/* 6087 * Find and write ARC buffers to the L2ARC device. 6088 * 6089 * An ARC_FLAG_L2_WRITING flag is set so that the L2ARC buffers are not valid 6090 * for reading until they have completed writing. 6091 * The headroom_boost is an in-out parameter used to maintain headroom boost 6092 * state between calls to this function. 6093 * 6094 * Returns the number of bytes actually written (which may be smaller than 6095 * the delta by which the device hand has changed due to alignment). 6096 */ 6097static uint64_t 6098l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz, 6099 boolean_t *headroom_boost) 6100{ 6101 arc_buf_hdr_t *hdr, *hdr_prev, *head; 6102 uint64_t write_asize, write_sz, headroom, buf_compress_minsz; 6103 void *buf_data; 6104 boolean_t full; 6105 l2arc_write_callback_t *cb; 6106 zio_t *pio, *wzio; 6107 uint64_t guid = spa_load_guid(spa); 6108 const boolean_t do_headroom_boost = *headroom_boost; 6109 int try; 6110 6111 ASSERT(dev->l2ad_vdev != NULL); 6112 6113 /* Lower the flag now, we might want to raise it again later. */ 6114 *headroom_boost = B_FALSE; 6115 6116 pio = NULL; 6117 write_sz = write_asize = 0; 6118 full = B_FALSE; 6119 head = kmem_cache_alloc(hdr_l2only_cache, KM_PUSHPAGE); 6120 head->b_flags |= ARC_FLAG_L2_WRITE_HEAD; 6121 head->b_flags |= ARC_FLAG_HAS_L2HDR; 6122 6123 ARCSTAT_BUMP(arcstat_l2_write_buffer_iter); 6124 /* 6125 * We will want to try to compress buffers that are at least 2x the 6126 * device sector size. 6127 */ 6128 buf_compress_minsz = 2 << dev->l2ad_vdev->vdev_ashift; 6129 6130 /* 6131 * Copy buffers for L2ARC writing. 6132 */ 6133 for (try = 0; try <= 3; try++) { 6134 multilist_sublist_t *mls = l2arc_sublist_lock(try); 6135 uint64_t passed_sz = 0; 6136 6137 ARCSTAT_BUMP(arcstat_l2_write_buffer_list_iter); 6138 6139 /* 6140 * L2ARC fast warmup. 6141 * 6142 * Until the ARC is warm and starts to evict, read from the 6143 * head of the ARC lists rather than the tail. 6144 */ 6145 if (arc_warm == B_FALSE) 6146 hdr = multilist_sublist_head(mls); 6147 else 6148 hdr = multilist_sublist_tail(mls); 6149 if (hdr == NULL) 6150 ARCSTAT_BUMP(arcstat_l2_write_buffer_list_null_iter); 6151 6152 headroom = target_sz * l2arc_headroom; 6153 if (do_headroom_boost) 6154 headroom = (headroom * l2arc_headroom_boost) / 100; 6155 6156 for (; hdr; hdr = hdr_prev) { 6157 kmutex_t *hash_lock; 6158 uint64_t buf_sz; 6159 uint64_t buf_a_sz; 6160 6161 if (arc_warm == B_FALSE) 6162 hdr_prev = multilist_sublist_next(mls, hdr); 6163 else 6164 hdr_prev = multilist_sublist_prev(mls, hdr); 6165 ARCSTAT_INCR(arcstat_l2_write_buffer_bytes_scanned, hdr->b_size); 6166 6167 hash_lock = HDR_LOCK(hdr); 6168 if (!mutex_tryenter(hash_lock)) { 6169 ARCSTAT_BUMP(arcstat_l2_write_trylock_fail); 6170 /* 6171 * Skip this buffer rather than waiting. 6172 */ 6173 continue; 6174 } 6175 6176 passed_sz += hdr->b_size; 6177 if (passed_sz > headroom) { 6178 /* 6179 * Searched too far. 6180 */ 6181 mutex_exit(hash_lock); 6182 ARCSTAT_BUMP(arcstat_l2_write_passed_headroom); 6183 break; 6184 } 6185 6186 if (!l2arc_write_eligible(guid, hdr)) { 6187 mutex_exit(hash_lock); 6188 continue; 6189 } 6190 6191 /* 6192 * Assume that the buffer is not going to be compressed 6193 * and could take more space on disk because of a larger 6194 * disk block size. 6195 */ 6196 buf_sz = hdr->b_size; 6197 buf_a_sz = vdev_psize_to_asize(dev->l2ad_vdev, buf_sz); 6198 6199 if ((write_asize + buf_a_sz) > target_sz) { 6200 full = B_TRUE; 6201 mutex_exit(hash_lock); 6202 ARCSTAT_BUMP(arcstat_l2_write_full); 6203 break; 6204 } 6205 6206 if (pio == NULL) { 6207 /* 6208 * Insert a dummy header on the buflist so 6209 * l2arc_write_done() can find where the 6210 * write buffers begin without searching. 6211 */ 6212 mutex_enter(&dev->l2ad_mtx); 6213 list_insert_head(&dev->l2ad_buflist, head); 6214 mutex_exit(&dev->l2ad_mtx); 6215 6216 cb = kmem_alloc( 6217 sizeof (l2arc_write_callback_t), KM_SLEEP); 6218 cb->l2wcb_dev = dev; 6219 cb->l2wcb_head = head; 6220 pio = zio_root(spa, l2arc_write_done, cb, 6221 ZIO_FLAG_CANFAIL); 6222 ARCSTAT_BUMP(arcstat_l2_write_pios); 6223 } 6224 6225 /* 6226 * Create and add a new L2ARC header. 6227 */ 6228 hdr->b_l2hdr.b_dev = dev; 6229 hdr->b_flags |= ARC_FLAG_L2_WRITING; 6230 /* 6231 * Temporarily stash the data buffer in b_tmp_cdata. 6232 * The subsequent write step will pick it up from 6233 * there. This is because can't access b_l1hdr.b_buf 6234 * without holding the hash_lock, which we in turn 6235 * can't access without holding the ARC list locks 6236 * (which we want to avoid during compression/writing). 6237 */ 6238 HDR_SET_COMPRESS(hdr, ZIO_COMPRESS_OFF); 6239 hdr->b_l2hdr.b_asize = hdr->b_size; 6240 hdr->b_l1hdr.b_tmp_cdata = hdr->b_l1hdr.b_buf->b_data; 6241 6242 /* 6243 * Explicitly set the b_daddr field to a known 6244 * value which means "invalid address". This 6245 * enables us to differentiate which stage of 6246 * l2arc_write_buffers() the particular header 6247 * is in (e.g. this loop, or the one below). 6248 * ARC_FLAG_L2_WRITING is not enough to make 6249 * this distinction, and we need to know in 6250 * order to do proper l2arc vdev accounting in 6251 * arc_release() and arc_hdr_destroy(). 6252 * 6253 * Note, we can't use a new flag to distinguish 6254 * the two stages because we don't hold the 6255 * header's hash_lock below, in the second stage 6256 * of this function. Thus, we can't simply 6257 * change the b_flags field to denote that the 6258 * IO has been sent. We can change the b_daddr 6259 * field of the L2 portion, though, since we'll 6260 * be holding the l2ad_mtx; which is why we're 6261 * using it to denote the header's state change. 6262 */ 6263 hdr->b_l2hdr.b_daddr = L2ARC_ADDR_UNSET; 6264 hdr->b_flags |= ARC_FLAG_HAS_L2HDR; 6265 6266 mutex_enter(&dev->l2ad_mtx); 6267 list_insert_head(&dev->l2ad_buflist, hdr); 6268 mutex_exit(&dev->l2ad_mtx); 6269 6270 /* 6271 * Compute and store the buffer cksum before 6272 * writing. On debug the cksum is verified first. 6273 */ 6274 arc_cksum_verify(hdr->b_l1hdr.b_buf); 6275 arc_cksum_compute(hdr->b_l1hdr.b_buf, B_TRUE); 6276 6277 mutex_exit(hash_lock); 6278 6279 write_sz += buf_sz; 6280 write_asize += buf_a_sz; 6281 } 6282 6283 multilist_sublist_unlock(mls); 6284 6285 if (full == B_TRUE) 6286 break; 6287 } 6288 6289 /* No buffers selected for writing? */ 6290 if (pio == NULL) { 6291 ASSERT0(write_sz); 6292 ASSERT(!HDR_HAS_L1HDR(head)); 6293 kmem_cache_free(hdr_l2only_cache, head); 6294 return (0); 6295 } 6296 6297 mutex_enter(&dev->l2ad_mtx); 6298 6299 /* 6300 * Note that elsewhere in this file arcstat_l2_asize 6301 * and the used space on l2ad_vdev are updated using b_asize, 6302 * which is not necessarily rounded up to the device block size. 6303 * Too keep accounting consistent we do the same here as well: 6304 * stats_size accumulates the sum of b_asize of the written buffers, 6305 * while write_asize accumulates the sum of b_asize rounded up 6306 * to the device block size. 6307 * The latter sum is used only to validate the corectness of the code. 6308 */ 6309 uint64_t stats_size = 0; 6310 write_asize = 0; 6311 6312 /* 6313 * Now start writing the buffers. We're starting at the write head 6314 * and work backwards, retracing the course of the buffer selector 6315 * loop above. 6316 */ 6317 for (hdr = list_prev(&dev->l2ad_buflist, head); hdr; 6318 hdr = list_prev(&dev->l2ad_buflist, hdr)) { 6319 uint64_t buf_sz; 6320 6321 /* 6322 * We rely on the L1 portion of the header below, so 6323 * it's invalid for this header to have been evicted out 6324 * of the ghost cache, prior to being written out. The 6325 * ARC_FLAG_L2_WRITING bit ensures this won't happen. 6326 */ 6327 ASSERT(HDR_HAS_L1HDR(hdr)); 6328 6329 /* 6330 * We shouldn't need to lock the buffer here, since we flagged 6331 * it as ARC_FLAG_L2_WRITING in the previous step, but we must 6332 * take care to only access its L2 cache parameters. In 6333 * particular, hdr->l1hdr.b_buf may be invalid by now due to 6334 * ARC eviction. 6335 */ 6336 hdr->b_l2hdr.b_daddr = dev->l2ad_hand; 6337 6338 if ((HDR_L2COMPRESS(hdr)) && 6339 hdr->b_l2hdr.b_asize >= buf_compress_minsz) { 6340 if (l2arc_compress_buf(hdr)) { 6341 /* 6342 * If compression succeeded, enable headroom 6343 * boost on the next scan cycle. 6344 */ 6345 *headroom_boost = B_TRUE; 6346 } 6347 } 6348 6349 /* 6350 * Pick up the buffer data we had previously stashed away 6351 * (and now potentially also compressed). 6352 */ 6353 buf_data = hdr->b_l1hdr.b_tmp_cdata; 6354 buf_sz = hdr->b_l2hdr.b_asize; 6355 6356 /* 6357 * If the data has not been compressed, then clear b_tmp_cdata 6358 * to make sure that it points only to a temporary compression 6359 * buffer. 6360 */ 6361 if (!L2ARC_IS_VALID_COMPRESS(HDR_GET_COMPRESS(hdr))) 6362 hdr->b_l1hdr.b_tmp_cdata = NULL; 6363 6364 /* 6365 * We need to do this regardless if buf_sz is zero or 6366 * not, otherwise, when this l2hdr is evicted we'll 6367 * remove a reference that was never added. 6368 */ 6369 (void) refcount_add_many(&dev->l2ad_alloc, buf_sz, hdr); 6370 6371 /* Compression may have squashed the buffer to zero length. */ 6372 if (buf_sz != 0) { 6373 uint64_t buf_a_sz; 6374 6375 wzio = zio_write_phys(pio, dev->l2ad_vdev, 6376 dev->l2ad_hand, buf_sz, buf_data, ZIO_CHECKSUM_OFF, 6377 NULL, NULL, ZIO_PRIORITY_ASYNC_WRITE, 6378 ZIO_FLAG_CANFAIL, B_FALSE); 6379 6380 DTRACE_PROBE2(l2arc__write, vdev_t *, dev->l2ad_vdev, 6381 zio_t *, wzio); 6382 (void) zio_nowait(wzio); 6383 6384 stats_size += buf_sz; 6385 6386 /* 6387 * Keep the clock hand suitably device-aligned. 6388 */ 6389 buf_a_sz = vdev_psize_to_asize(dev->l2ad_vdev, buf_sz); 6390 write_asize += buf_a_sz; 6391 dev->l2ad_hand += buf_a_sz; 6392 } 6393 } 6394 6395 mutex_exit(&dev->l2ad_mtx); 6396 6397 ASSERT3U(write_asize, <=, target_sz); 6398 ARCSTAT_BUMP(arcstat_l2_writes_sent); 6399 ARCSTAT_INCR(arcstat_l2_write_bytes, write_asize); 6400 ARCSTAT_INCR(arcstat_l2_size, write_sz); 6401 ARCSTAT_INCR(arcstat_l2_asize, stats_size); 6402 vdev_space_update(dev->l2ad_vdev, stats_size, 0, 0); 6403 6404 /* 6405 * Bump device hand to the device start if it is approaching the end. 6406 * l2arc_evict() will already have evicted ahead for this case. 6407 */ 6408 if (dev->l2ad_hand >= (dev->l2ad_end - target_sz)) { 6409 dev->l2ad_hand = dev->l2ad_start; 6410 dev->l2ad_first = B_FALSE; 6411 } 6412 6413 dev->l2ad_writing = B_TRUE; 6414 (void) zio_wait(pio); 6415 dev->l2ad_writing = B_FALSE; 6416 6417 return (write_asize); 6418} 6419 6420/* 6421 * Compresses an L2ARC buffer. 6422 * The data to be compressed must be prefilled in l1hdr.b_tmp_cdata and its 6423 * size in l2hdr->b_asize. This routine tries to compress the data and 6424 * depending on the compression result there are three possible outcomes: 6425 * *) The buffer was incompressible. The original l2hdr contents were left 6426 * untouched and are ready for writing to an L2 device. 6427 * *) The buffer was all-zeros, so there is no need to write it to an L2 6428 * device. To indicate this situation b_tmp_cdata is NULL'ed, b_asize is 6429 * set to zero and b_compress is set to ZIO_COMPRESS_EMPTY. 6430 * *) Compression succeeded and b_tmp_cdata was replaced with a temporary 6431 * data buffer which holds the compressed data to be written, and b_asize 6432 * tells us how much data there is. b_compress is set to the appropriate 6433 * compression algorithm. Once writing is done, invoke 6434 * l2arc_release_cdata_buf on this l2hdr to free this temporary buffer. 6435 * 6436 * Returns B_TRUE if compression succeeded, or B_FALSE if it didn't (the 6437 * buffer was incompressible). 6438 */ 6439static boolean_t 6440l2arc_compress_buf(arc_buf_hdr_t *hdr) 6441{ 6442 void *cdata; 6443 size_t csize, len, rounded; 6444 ASSERT(HDR_HAS_L2HDR(hdr)); 6445 l2arc_buf_hdr_t *l2hdr = &hdr->b_l2hdr; 6446 6447 ASSERT(HDR_HAS_L1HDR(hdr)); 6448 ASSERT(HDR_GET_COMPRESS(hdr) == ZIO_COMPRESS_OFF); 6449 ASSERT(hdr->b_l1hdr.b_tmp_cdata != NULL); 6450 6451 len = l2hdr->b_asize; 6452 cdata = zio_data_buf_alloc(len); 6453 ASSERT3P(cdata, !=, NULL); 6454 csize = zio_compress_data(ZIO_COMPRESS_LZ4, hdr->b_l1hdr.b_tmp_cdata, 6455 cdata, l2hdr->b_asize); 6456 6457 if (csize == 0) { 6458 /* zero block, indicate that there's nothing to write */ 6459 zio_data_buf_free(cdata, len); 6460 HDR_SET_COMPRESS(hdr, ZIO_COMPRESS_EMPTY); 6461 l2hdr->b_asize = 0; 6462 hdr->b_l1hdr.b_tmp_cdata = NULL; 6463 ARCSTAT_BUMP(arcstat_l2_compress_zeros); 6464 return (B_TRUE); 6465 } 6466 6467 rounded = P2ROUNDUP(csize, 6468 (size_t)1 << l2hdr->b_dev->l2ad_vdev->vdev_ashift); 6469 if (rounded < len) { 6470 /* 6471 * Compression succeeded, we'll keep the cdata around for 6472 * writing and release it afterwards. 6473 */ 6474 if (rounded > csize) { 6475 bzero((char *)cdata + csize, rounded - csize); 6476 csize = rounded; 6477 } 6478 HDR_SET_COMPRESS(hdr, ZIO_COMPRESS_LZ4); 6479 l2hdr->b_asize = csize; 6480 hdr->b_l1hdr.b_tmp_cdata = cdata; 6481 ARCSTAT_BUMP(arcstat_l2_compress_successes); 6482 return (B_TRUE); 6483 } else { 6484 /* 6485 * Compression failed, release the compressed buffer. 6486 * l2hdr will be left unmodified. 6487 */ 6488 zio_data_buf_free(cdata, len); 6489 ARCSTAT_BUMP(arcstat_l2_compress_failures); 6490 return (B_FALSE); 6491 } 6492} 6493 6494/* 6495 * Decompresses a zio read back from an l2arc device. On success, the 6496 * underlying zio's io_data buffer is overwritten by the uncompressed 6497 * version. On decompression error (corrupt compressed stream), the 6498 * zio->io_error value is set to signal an I/O error. 6499 * 6500 * Please note that the compressed data stream is not checksummed, so 6501 * if the underlying device is experiencing data corruption, we may feed 6502 * corrupt data to the decompressor, so the decompressor needs to be 6503 * able to handle this situation (LZ4 does). 6504 */ 6505static void 6506l2arc_decompress_zio(zio_t *zio, arc_buf_hdr_t *hdr, enum zio_compress c) 6507{ 6508 ASSERT(L2ARC_IS_VALID_COMPRESS(c)); 6509 6510 if (zio->io_error != 0) { 6511 /* 6512 * An io error has occured, just restore the original io 6513 * size in preparation for a main pool read. 6514 */ 6515 zio->io_orig_size = zio->io_size = hdr->b_size; 6516 return; 6517 } 6518 6519 if (c == ZIO_COMPRESS_EMPTY) { 6520 /* 6521 * An empty buffer results in a null zio, which means we 6522 * need to fill its io_data after we're done restoring the 6523 * buffer's contents. 6524 */ 6525 ASSERT(hdr->b_l1hdr.b_buf != NULL); 6526 bzero(hdr->b_l1hdr.b_buf->b_data, hdr->b_size); 6527 zio->io_data = zio->io_orig_data = hdr->b_l1hdr.b_buf->b_data; 6528 } else { 6529 ASSERT(zio->io_data != NULL); 6530 /* 6531 * We copy the compressed data from the start of the arc buffer 6532 * (the zio_read will have pulled in only what we need, the 6533 * rest is garbage which we will overwrite at decompression) 6534 * and then decompress back to the ARC data buffer. This way we 6535 * can minimize copying by simply decompressing back over the 6536 * original compressed data (rather than decompressing to an 6537 * aux buffer and then copying back the uncompressed buffer, 6538 * which is likely to be much larger). 6539 */ 6540 uint64_t csize; 6541 void *cdata; 6542 6543 csize = zio->io_size; 6544 cdata = zio_data_buf_alloc(csize); 6545 bcopy(zio->io_data, cdata, csize); 6546 if (zio_decompress_data(c, cdata, zio->io_data, csize, 6547 hdr->b_size) != 0) 6548 zio->io_error = EIO; 6549 zio_data_buf_free(cdata, csize); 6550 } 6551 6552 /* Restore the expected uncompressed IO size. */ 6553 zio->io_orig_size = zio->io_size = hdr->b_size; 6554} 6555 6556/* 6557 * Releases the temporary b_tmp_cdata buffer in an l2arc header structure. 6558 * This buffer serves as a temporary holder of compressed data while 6559 * the buffer entry is being written to an l2arc device. Once that is 6560 * done, we can dispose of it. 6561 */ 6562static void 6563l2arc_release_cdata_buf(arc_buf_hdr_t *hdr) 6564{ 6565 enum zio_compress comp = HDR_GET_COMPRESS(hdr); 6566 6567 ASSERT(HDR_HAS_L1HDR(hdr)); 6568 ASSERT(comp == ZIO_COMPRESS_OFF || L2ARC_IS_VALID_COMPRESS(comp)); 6569 6570 if (comp == ZIO_COMPRESS_OFF) { 6571 /* 6572 * In this case, b_tmp_cdata points to the same buffer 6573 * as the arc_buf_t's b_data field. We don't want to 6574 * free it, since the arc_buf_t will handle that. 6575 */ 6576 hdr->b_l1hdr.b_tmp_cdata = NULL; 6577 } else if (comp == ZIO_COMPRESS_EMPTY) { 6578 /* 6579 * In this case, b_tmp_cdata was compressed to an empty 6580 * buffer, thus there's nothing to free and b_tmp_cdata 6581 * should have been set to NULL in l2arc_write_buffers(). 6582 */ 6583 ASSERT3P(hdr->b_l1hdr.b_tmp_cdata, ==, NULL); 6584 } else { 6585 /* 6586 * If the data was compressed, then we've allocated a 6587 * temporary buffer for it, so now we need to release it. 6588 */ 6589 ASSERT(hdr->b_l1hdr.b_tmp_cdata != NULL); 6590 zio_data_buf_free(hdr->b_l1hdr.b_tmp_cdata, 6591 hdr->b_size); 6592 hdr->b_l1hdr.b_tmp_cdata = NULL; 6593 } 6594} 6595 6596/* 6597 * This thread feeds the L2ARC at regular intervals. This is the beating 6598 * heart of the L2ARC. 6599 */ 6600static void 6601l2arc_feed_thread(void *dummy __unused) 6602{ 6603 callb_cpr_t cpr; 6604 l2arc_dev_t *dev; 6605 spa_t *spa; 6606 uint64_t size, wrote; 6607 clock_t begin, next = ddi_get_lbolt(); 6608 boolean_t headroom_boost = B_FALSE; 6609 6610 CALLB_CPR_INIT(&cpr, &l2arc_feed_thr_lock, callb_generic_cpr, FTAG); 6611 6612 mutex_enter(&l2arc_feed_thr_lock); 6613 6614 while (l2arc_thread_exit == 0) { 6615 CALLB_CPR_SAFE_BEGIN(&cpr); 6616 (void) cv_timedwait(&l2arc_feed_thr_cv, &l2arc_feed_thr_lock, 6617 next - ddi_get_lbolt()); 6618 CALLB_CPR_SAFE_END(&cpr, &l2arc_feed_thr_lock); 6619 next = ddi_get_lbolt() + hz; 6620 6621 /* 6622 * Quick check for L2ARC devices. 6623 */ 6624 mutex_enter(&l2arc_dev_mtx); 6625 if (l2arc_ndev == 0) { 6626 mutex_exit(&l2arc_dev_mtx); 6627 continue; 6628 } 6629 mutex_exit(&l2arc_dev_mtx); 6630 begin = ddi_get_lbolt(); 6631 6632 /* 6633 * This selects the next l2arc device to write to, and in 6634 * doing so the next spa to feed from: dev->l2ad_spa. This 6635 * will return NULL if there are now no l2arc devices or if 6636 * they are all faulted. 6637 * 6638 * If a device is returned, its spa's config lock is also 6639 * held to prevent device removal. l2arc_dev_get_next() 6640 * will grab and release l2arc_dev_mtx. 6641 */ 6642 if ((dev = l2arc_dev_get_next()) == NULL) 6643 continue; 6644 6645 spa = dev->l2ad_spa; 6646 ASSERT(spa != NULL); 6647 6648 /* 6649 * If the pool is read-only then force the feed thread to 6650 * sleep a little longer. 6651 */ 6652 if (!spa_writeable(spa)) { 6653 next = ddi_get_lbolt() + 5 * l2arc_feed_secs * hz; 6654 spa_config_exit(spa, SCL_L2ARC, dev); 6655 continue; 6656 } 6657 6658 /* 6659 * Avoid contributing to memory pressure. 6660 */ 6661 if (arc_reclaim_needed()) { 6662 ARCSTAT_BUMP(arcstat_l2_abort_lowmem); 6663 spa_config_exit(spa, SCL_L2ARC, dev); 6664 continue; 6665 } 6666 6667 ARCSTAT_BUMP(arcstat_l2_feeds); 6668 6669 size = l2arc_write_size(); 6670 6671 /* 6672 * Evict L2ARC buffers that will be overwritten. 6673 */ 6674 l2arc_evict(dev, size, B_FALSE); 6675 6676 /* 6677 * Write ARC buffers. 6678 */ 6679 wrote = l2arc_write_buffers(spa, dev, size, &headroom_boost); 6680 6681 /* 6682 * Calculate interval between writes. 6683 */ 6684 next = l2arc_write_interval(begin, size, wrote); 6685 spa_config_exit(spa, SCL_L2ARC, dev); 6686 } 6687 6688 l2arc_thread_exit = 0; 6689 cv_broadcast(&l2arc_feed_thr_cv); 6690 CALLB_CPR_EXIT(&cpr); /* drops l2arc_feed_thr_lock */ 6691 thread_exit(); 6692} 6693 6694boolean_t 6695l2arc_vdev_present(vdev_t *vd) 6696{ 6697 l2arc_dev_t *dev; 6698 6699 mutex_enter(&l2arc_dev_mtx); 6700 for (dev = list_head(l2arc_dev_list); dev != NULL; 6701 dev = list_next(l2arc_dev_list, dev)) { 6702 if (dev->l2ad_vdev == vd) 6703 break; 6704 } 6705 mutex_exit(&l2arc_dev_mtx); 6706 6707 return (dev != NULL); 6708} 6709 6710/* 6711 * Add a vdev for use by the L2ARC. By this point the spa has already 6712 * validated the vdev and opened it. 6713 */ 6714void 6715l2arc_add_vdev(spa_t *spa, vdev_t *vd) 6716{ 6717 l2arc_dev_t *adddev; 6718 6719 ASSERT(!l2arc_vdev_present(vd)); 6720 6721 vdev_ashift_optimize(vd); 6722 6723 /* 6724 * Create a new l2arc device entry. 6725 */ 6726 adddev = kmem_zalloc(sizeof (l2arc_dev_t), KM_SLEEP); 6727 adddev->l2ad_spa = spa; 6728 adddev->l2ad_vdev = vd; 6729 adddev->l2ad_start = VDEV_LABEL_START_SIZE; 6730 adddev->l2ad_end = VDEV_LABEL_START_SIZE + vdev_get_min_asize(vd); 6731 adddev->l2ad_hand = adddev->l2ad_start; 6732 adddev->l2ad_first = B_TRUE; 6733 adddev->l2ad_writing = B_FALSE; 6734 6735 mutex_init(&adddev->l2ad_mtx, NULL, MUTEX_DEFAULT, NULL); 6736 /* 6737 * This is a list of all ARC buffers that are still valid on the 6738 * device. 6739 */ 6740 list_create(&adddev->l2ad_buflist, sizeof (arc_buf_hdr_t), 6741 offsetof(arc_buf_hdr_t, b_l2hdr.b_l2node)); 6742 6743 vdev_space_update(vd, 0, 0, adddev->l2ad_end - adddev->l2ad_hand); 6744 refcount_create(&adddev->l2ad_alloc); 6745 6746 /* 6747 * Add device to global list 6748 */ 6749 mutex_enter(&l2arc_dev_mtx); 6750 list_insert_head(l2arc_dev_list, adddev); 6751 atomic_inc_64(&l2arc_ndev); 6752 mutex_exit(&l2arc_dev_mtx); 6753} 6754 6755/* 6756 * Remove a vdev from the L2ARC. 6757 */ 6758void 6759l2arc_remove_vdev(vdev_t *vd) 6760{ 6761 l2arc_dev_t *dev, *nextdev, *remdev = NULL; 6762 6763 /* 6764 * Find the device by vdev 6765 */ 6766 mutex_enter(&l2arc_dev_mtx); 6767 for (dev = list_head(l2arc_dev_list); dev; dev = nextdev) { 6768 nextdev = list_next(l2arc_dev_list, dev); 6769 if (vd == dev->l2ad_vdev) { 6770 remdev = dev; 6771 break; 6772 } 6773 } 6774 ASSERT(remdev != NULL); 6775 6776 /* 6777 * Remove device from global list 6778 */ 6779 list_remove(l2arc_dev_list, remdev); 6780 l2arc_dev_last = NULL; /* may have been invalidated */ 6781 atomic_dec_64(&l2arc_ndev); 6782 mutex_exit(&l2arc_dev_mtx); 6783 6784 /* 6785 * Clear all buflists and ARC references. L2ARC device flush. 6786 */ 6787 l2arc_evict(remdev, 0, B_TRUE); 6788 list_destroy(&remdev->l2ad_buflist); 6789 mutex_destroy(&remdev->l2ad_mtx); 6790 refcount_destroy(&remdev->l2ad_alloc); 6791 kmem_free(remdev, sizeof (l2arc_dev_t)); 6792} 6793 6794void 6795l2arc_init(void) 6796{ 6797 l2arc_thread_exit = 0; 6798 l2arc_ndev = 0; 6799 l2arc_writes_sent = 0; 6800 l2arc_writes_done = 0; 6801 6802 mutex_init(&l2arc_feed_thr_lock, NULL, MUTEX_DEFAULT, NULL); 6803 cv_init(&l2arc_feed_thr_cv, NULL, CV_DEFAULT, NULL); 6804 mutex_init(&l2arc_dev_mtx, NULL, MUTEX_DEFAULT, NULL); 6805 mutex_init(&l2arc_free_on_write_mtx, NULL, MUTEX_DEFAULT, NULL); 6806 6807 l2arc_dev_list = &L2ARC_dev_list; 6808 l2arc_free_on_write = &L2ARC_free_on_write; 6809 list_create(l2arc_dev_list, sizeof (l2arc_dev_t), 6810 offsetof(l2arc_dev_t, l2ad_node)); 6811 list_create(l2arc_free_on_write, sizeof (l2arc_data_free_t), 6812 offsetof(l2arc_data_free_t, l2df_list_node)); 6813} 6814 6815void 6816l2arc_fini(void) 6817{ 6818 /* 6819 * This is called from dmu_fini(), which is called from spa_fini(); 6820 * Because of this, we can assume that all l2arc devices have 6821 * already been removed when the pools themselves were removed. 6822 */ 6823 6824 l2arc_do_free_on_write(); 6825 6826 mutex_destroy(&l2arc_feed_thr_lock); 6827 cv_destroy(&l2arc_feed_thr_cv); 6828 mutex_destroy(&l2arc_dev_mtx); 6829 mutex_destroy(&l2arc_free_on_write_mtx); 6830 6831 list_destroy(l2arc_dev_list); 6832 list_destroy(l2arc_free_on_write); 6833} 6834 6835void 6836l2arc_start(void) 6837{ 6838 if (!(spa_mode_global & FWRITE)) 6839 return; 6840 6841 (void) thread_create(NULL, 0, l2arc_feed_thread, NULL, 0, &p0, 6842 TS_RUN, minclsyspri); 6843} 6844 6845void 6846l2arc_stop(void) 6847{ 6848 if (!(spa_mode_global & FWRITE)) 6849 return; 6850 6851 mutex_enter(&l2arc_feed_thr_lock); 6852 cv_signal(&l2arc_feed_thr_cv); /* kick thread out of startup */ 6853 l2arc_thread_exit = 1; 6854 while (l2arc_thread_exit != 0) 6855 cv_wait(&l2arc_feed_thr_cv, &l2arc_feed_thr_lock); 6856 mutex_exit(&l2arc_feed_thr_lock); 6857} 6858