cache_config.c revision 299742 
1/* svn_cache_config.c : configuration of internal caches
2 *
3 * ====================================================================
4 *    Licensed to the Apache Software Foundation (ASF) under one
5 *    or more contributor license agreements.  See the NOTICE file
6 *    distributed with this work for additional information
7 *    regarding copyright ownership.  The ASF licenses this file
8 *    to you under the Apache License, Version 2.0 (the
9 *    "License"); you may not use this file except in compliance
10 *    with the License.  You may obtain a copy of the License at
11 *
12 *      http://www.apache.org/licenses/LICENSE-2.0
13 *
14 *    Unless required by applicable law or agreed to in writing,
15 *    software distributed under the License is distributed on an
16 *    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
17 *    KIND, either express or implied.  See the License for the
18 *    specific language governing permissions and limitations
19 *    under the License.
20 * ====================================================================
21 */
22
23#include <apr_atomic.h>
24
25#include "svn_cache_config.h"
26#include "private/svn_atomic.h"
27#include "private/svn_cache.h"
28
29#include "svn_pools.h"
30#include "svn_sorts.h"
31
32/* The cache settings as a process-wide singleton.
33 */
34static svn_cache_config_t cache_settings =
35  {
36    /* default configuration:
37     *
38     * Please note that the resources listed below will be allocated
39     * PER PROCESS. Thus, the defaults chosen here are kept deliberately
40     * low to still make a difference yet to ensure that pre-fork servers
41     * on machines with small amounts of RAM aren't severely impacted.
42     */
43    0x1000000,   /* 16 MB for caches.
44                  * If you are running a single server process,
45                  * you may easily increase that to 50+% of your RAM
46                  * using svn_fs_set_cache_config().
47                  */
48    16,          /* up to 16 files kept open.
49                  * Most OS restrict the number of open file handles to
50                  * about 1000. To minimize I/O and OS overhead, values
51                  * of 500+ can be beneficial (use svn_fs_set_cache_config()
52                  * to change the configuration).
53                  * When running with a huge in-process cache, this number
54                  * has little impact on performance and a more modest
55                  * value (< 100) may be more suitable.
56                  */
57#if APR_HAS_THREADS
58    FALSE        /* assume multi-threaded operation.
59                  * Because this simply activates proper synchronization
60                  * between threads, it is a safe default.
61                  */
62#else
63    TRUE         /* single-threaded is the only supported mode of operation */
64#endif
65};
66
67/* Get the current FSFS cache configuration. */
68const svn_cache_config_t *
69svn_cache_config_get(void)
70{
71  return &cache_settings;
72}
73
74/* Initializer function as required by svn_atomic__init_once.  Allocate
75 * the process-global (singleton) membuffer cache and return it in the
76 * svn_membuffer_t * in *BATON.  UNUSED_POOL is unused and should be NULL.
77 */
78static svn_error_t *
79initialize_cache(void *baton, apr_pool_t *unused_pool)
80{
81  svn_membuffer_t **cache_p = baton;
82  svn_membuffer_t *cache = NULL;
83
84  /* Limit the cache size to about half the available address space
85   * (typ. 1G under 32 bits).
86   */
87  apr_uint64_t cache_size = MIN(cache_settings.cache_size,
88                                (apr_uint64_t)SVN_MAX_OBJECT_SIZE / 2);
89
90  /* Create caches at all? */
91  if (cache_size)
92    {
93      svn_error_t *err;
94
95      /* auto-allocate cache */
96      apr_allocator_t *allocator = NULL;
97      apr_pool_t *pool = NULL;
98
99      if (apr_allocator_create(&allocator))
100        return SVN_NO_ERROR;
101
102      /* Ensure that we free partially allocated data if we run OOM
103       * before the cache is complete: If the cache cannot be allocated
104       * in its full size, the create() function will clear the pool
105       * explicitly. The allocator will make sure that any memory no
106       * longer used by the pool will actually be returned to the OS.
107       *
108       * Please note that this pool and allocator is used *only* to
109       * allocate the large membuffer. All later dynamic allocations
110       * come from other, temporary pools and allocators.
111       */
112      apr_allocator_max_free_set(allocator, 1);
113
114      /* don't terminate upon OOM but make pool return a NULL pointer
115       * instead so we can disable caching gracefully and continue
116       * operation without membuffer caches.
117       */
118      apr_pool_create_ex(&pool, NULL, NULL, allocator);
119      if (pool == NULL)
120        return SVN_NO_ERROR;
121      apr_allocator_owner_set(allocator, pool);
122
123      err = svn_cache__membuffer_cache_create(
124          &cache,
125          (apr_size_t)cache_size,
126          (apr_size_t)(cache_size / 5),
127          0,
128          ! svn_cache_config_get()->single_threaded,
129          FALSE,
130          pool);
131
132      /* Some error occurred. Most likely it's an OOM error but we don't
133       * really care. Simply release all cache memory and disable caching
134       */
135      if (err)
136        {
137          /* Memory cleanup */
138          svn_pool_destroy(pool);
139
140          /* Document that we actually don't have a cache. */
141          cache_settings.cache_size = 0;
142
143          return svn_error_trace(err);
144        }
145
146      /* done */
147      *cache_p = cache;
148    }
149
150  return SVN_NO_ERROR;
151}
152
153/* Access the process-global (singleton) membuffer cache. The first call
154 * will automatically allocate the cache using the current cache config.
155 * NULL will be returned if the desired cache size is 0 or if the cache
156 * could not be created for some reason.
157 */
158svn_membuffer_t *
159svn_cache__get_global_membuffer_cache(void)
160{
161  static svn_membuffer_t *cache = NULL;
162  static svn_atomic_t initialized = 0;
163
164  svn_error_t *err
165    = svn_atomic__init_once(&initialized, initialize_cache, &cache, NULL);
166  if (err)
167    {
168      /* no caches today ... */
169      svn_error_clear(err);
170      return NULL;
171    }
172
173  return cache;
174}
175
176void
177svn_cache_config_set(const svn_cache_config_t *settings)
178{
179  cache_settings = *settings;
180}
181
182