dmu_zfetch.c revision 288594
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 2009 Sun Microsystems, Inc. All rights reserved. 23 * Use is subject to license terms. 24 */ 25 26/* 27 * Copyright (c) 2013, 2014 by Delphix. All rights reserved. 28 */ 29 30#include <sys/zfs_context.h> 31#include <sys/dnode.h> 32#include <sys/dmu_objset.h> 33#include <sys/dmu_zfetch.h> 34#include <sys/dmu.h> 35#include <sys/dbuf.h> 36#include <sys/kstat.h> 37 38/* 39 * This tunable disables predictive prefetch. Note that it leaves "prescient" 40 * prefetch (e.g. prefetch for zfs send) intact. Unlike predictive prefetch, 41 * prescient prefetch never issues i/os that end up not being needed, 42 * so it can't hurt performance. 43 */ 44boolean_t zfs_prefetch_disable = B_FALSE; 45 46/* max # of streams per zfetch */ 47uint32_t zfetch_max_streams = 8; 48/* min time before stream reclaim */ 49uint32_t zfetch_min_sec_reap = 2; 50/* max bytes to prefetch per stream (default 8MB) */ 51uint32_t zfetch_max_distance = 8 * 1024 * 1024; 52/* number of bytes in a array_read at which we stop prefetching (1MB) */ 53uint64_t zfetch_array_rd_sz = 1024 * 1024; 54 55SYSCTL_DECL(_vfs_zfs); 56SYSCTL_INT(_vfs_zfs, OID_AUTO, prefetch_disable, CTLFLAG_RW, 57 &zfs_prefetch_disable, 0, "Disable prefetch"); 58SYSCTL_NODE(_vfs_zfs, OID_AUTO, zfetch, CTLFLAG_RW, 0, "ZFS ZFETCH"); 59TUNABLE_INT("vfs.zfs.zfetch.max_streams", &zfetch_max_streams); 60SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, max_streams, CTLFLAG_RW, 61 &zfetch_max_streams, 0, "Max # of streams per zfetch"); 62TUNABLE_INT("vfs.zfs.zfetch.min_sec_reap", &zfetch_min_sec_reap); 63SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, min_sec_reap, CTLFLAG_RWTUN, 64 &zfetch_min_sec_reap, 0, "Min time before stream reclaim"); 65TUNABLE_INT("vfs.zfs.zfetch.max_distance", &zfetch_max_distance); 66SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, max_distance, CTLFLAG_RWTUN, 67 &zfetch_max_distance, 0, "Max bytes to prefetch per stream"); 68TUNABLE_QUAD("vfs.zfs.zfetch.array_rd_sz", &zfetch_array_rd_sz); 69SYSCTL_UQUAD(_vfs_zfs_zfetch, OID_AUTO, array_rd_sz, CTLFLAG_RWTUN, 70 &zfetch_array_rd_sz, 0, 71 "Number of bytes in a array_read at which we stop prefetching"); 72 73typedef struct zfetch_stats { 74 kstat_named_t zfetchstat_hits; 75 kstat_named_t zfetchstat_misses; 76 kstat_named_t zfetchstat_max_streams; 77} zfetch_stats_t; 78 79static zfetch_stats_t zfetch_stats = { 80 { "hits", KSTAT_DATA_UINT64 }, 81 { "misses", KSTAT_DATA_UINT64 }, 82 { "max_streams", KSTAT_DATA_UINT64 }, 83}; 84 85#define ZFETCHSTAT_BUMP(stat) \ 86 atomic_inc_64(&zfetch_stats.stat.value.ui64); 87 88kstat_t *zfetch_ksp; 89 90void 91zfetch_init(void) 92{ 93 zfetch_ksp = kstat_create("zfs", 0, "zfetchstats", "misc", 94 KSTAT_TYPE_NAMED, sizeof (zfetch_stats) / sizeof (kstat_named_t), 95 KSTAT_FLAG_VIRTUAL); 96 97 if (zfetch_ksp != NULL) { 98 zfetch_ksp->ks_data = &zfetch_stats; 99 kstat_install(zfetch_ksp); 100 } 101} 102 103void 104zfetch_fini(void) 105{ 106 if (zfetch_ksp != NULL) { 107 kstat_delete(zfetch_ksp); 108 zfetch_ksp = NULL; 109 } 110} 111 112/* 113 * This takes a pointer to a zfetch structure and a dnode. It performs the 114 * necessary setup for the zfetch structure, grokking data from the 115 * associated dnode. 116 */ 117void 118dmu_zfetch_init(zfetch_t *zf, dnode_t *dno) 119{ 120 if (zf == NULL) 121 return; 122 123 zf->zf_dnode = dno; 124 125 list_create(&zf->zf_stream, sizeof (zstream_t), 126 offsetof(zstream_t, zs_node)); 127 128 rw_init(&zf->zf_rwlock, NULL, RW_DEFAULT, NULL); 129} 130 131static void 132dmu_zfetch_stream_remove(zfetch_t *zf, zstream_t *zs) 133{ 134 ASSERT(RW_WRITE_HELD(&zf->zf_rwlock)); 135 list_remove(&zf->zf_stream, zs); 136 mutex_destroy(&zs->zs_lock); 137 kmem_free(zs, sizeof (*zs)); 138} 139 140/* 141 * Clean-up state associated with a zfetch structure (e.g. destroy the 142 * streams). This doesn't free the zfetch_t itself, that's left to the caller. 143 */ 144void 145dmu_zfetch_fini(zfetch_t *zf) 146{ 147 zstream_t *zs; 148 149 ASSERT(!RW_LOCK_HELD(&zf->zf_rwlock)); 150 151 rw_enter(&zf->zf_rwlock, RW_WRITER); 152 while ((zs = list_head(&zf->zf_stream)) != NULL) 153 dmu_zfetch_stream_remove(zf, zs); 154 rw_exit(&zf->zf_rwlock); 155 list_destroy(&zf->zf_stream); 156 rw_destroy(&zf->zf_rwlock); 157 158 zf->zf_dnode = NULL; 159} 160 161/* 162 * If there aren't too many streams already, create a new stream. 163 * The "blkid" argument is the next block that we expect this stream to access. 164 * While we're here, clean up old streams (which haven't been 165 * accessed for at least zfetch_min_sec_reap seconds). 166 */ 167static void 168dmu_zfetch_stream_create(zfetch_t *zf, uint64_t blkid) 169{ 170 zstream_t *zs_next; 171 int numstreams = 0; 172 173 ASSERT(RW_WRITE_HELD(&zf->zf_rwlock)); 174 175 /* 176 * Clean up old streams. 177 */ 178 for (zstream_t *zs = list_head(&zf->zf_stream); 179 zs != NULL; zs = zs_next) { 180 zs_next = list_next(&zf->zf_stream, zs); 181 if (((gethrtime() - zs->zs_atime) / NANOSEC) > 182 zfetch_min_sec_reap) 183 dmu_zfetch_stream_remove(zf, zs); 184 else 185 numstreams++; 186 } 187 188 /* 189 * The maximum number of streams is normally zfetch_max_streams, 190 * but for small files we lower it such that it's at least possible 191 * for all the streams to be non-overlapping. 192 * 193 * If we are already at the maximum number of streams for this file, 194 * even after removing old streams, then don't create this stream. 195 */ 196 uint32_t max_streams = MAX(1, MIN(zfetch_max_streams, 197 zf->zf_dnode->dn_maxblkid * zf->zf_dnode->dn_datablksz / 198 zfetch_max_distance)); 199 if (numstreams >= max_streams) { 200 ZFETCHSTAT_BUMP(zfetchstat_max_streams); 201 return; 202 } 203 204 zstream_t *zs = kmem_zalloc(sizeof (*zs), KM_SLEEP); 205 zs->zs_blkid = blkid; 206 zs->zs_pf_blkid = blkid; 207 zs->zs_atime = gethrtime(); 208 mutex_init(&zs->zs_lock, NULL, MUTEX_DEFAULT, NULL); 209 210 list_insert_head(&zf->zf_stream, zs); 211} 212 213/* 214 * This is the prefetch entry point. It calls all of the other dmu_zfetch 215 * routines to create, delete, find, or operate upon prefetch streams. 216 */ 217void 218dmu_zfetch(zfetch_t *zf, uint64_t blkid, uint64_t nblks) 219{ 220 zstream_t *zs; 221 222 if (zfs_prefetch_disable) 223 return; 224 225 /* 226 * As a fast path for small (single-block) files, ignore access 227 * to the first block. 228 */ 229 if (blkid == 0) 230 return; 231 232 rw_enter(&zf->zf_rwlock, RW_READER); 233 234 for (zs = list_head(&zf->zf_stream); zs != NULL; 235 zs = list_next(&zf->zf_stream, zs)) { 236 if (blkid == zs->zs_blkid) { 237 mutex_enter(&zs->zs_lock); 238 /* 239 * zs_blkid could have changed before we 240 * acquired zs_lock; re-check them here. 241 */ 242 if (blkid != zs->zs_blkid) { 243 mutex_exit(&zs->zs_lock); 244 continue; 245 } 246 break; 247 } 248 } 249 250 if (zs == NULL) { 251 /* 252 * This access is not part of any existing stream. Create 253 * a new stream for it. 254 */ 255 ZFETCHSTAT_BUMP(zfetchstat_misses); 256 if (rw_tryupgrade(&zf->zf_rwlock)) 257 dmu_zfetch_stream_create(zf, blkid + nblks); 258 rw_exit(&zf->zf_rwlock); 259 return; 260 } 261 262 /* 263 * This access was to a block that we issued a prefetch for on 264 * behalf of this stream. Issue further prefetches for this stream. 265 * 266 * Normally, we start prefetching where we stopped 267 * prefetching last (zs_pf_blkid). But when we get our first 268 * hit on this stream, zs_pf_blkid == zs_blkid, we don't 269 * want to prefetch to block we just accessed. In this case, 270 * start just after the block we just accessed. 271 */ 272 int64_t pf_start = MAX(zs->zs_pf_blkid, blkid + nblks); 273 274 /* 275 * Double our amount of prefetched data, but don't let the 276 * prefetch get further ahead than zfetch_max_distance. 277 */ 278 int pf_nblks = 279 MIN((int64_t)zs->zs_pf_blkid - zs->zs_blkid + nblks, 280 zs->zs_blkid + nblks + 281 (zfetch_max_distance >> zf->zf_dnode->dn_datablkshift) - pf_start); 282 283 zs->zs_pf_blkid = pf_start + pf_nblks; 284 zs->zs_atime = gethrtime(); 285 zs->zs_blkid = blkid + nblks; 286 287 /* 288 * dbuf_prefetch() issues the prefetch i/o 289 * asynchronously, but it may need to wait for an 290 * indirect block to be read from disk. Therefore 291 * we do not want to hold any locks while we call it. 292 */ 293 mutex_exit(&zs->zs_lock); 294 rw_exit(&zf->zf_rwlock); 295 for (int i = 0; i < pf_nblks; i++) { 296 dbuf_prefetch(zf->zf_dnode, 0, pf_start + i, 297 ZIO_PRIORITY_ASYNC_READ, ARC_FLAG_PREDICTIVE_PREFETCH); 298 } 299 ZFETCHSTAT_BUMP(zfetchstat_hits); 300} 301