subversion/libsvn_subr/cache_config.c

   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  */
  34 static 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. */
  68 const svn_cache_config_t *
  69 svn_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  */
  78 static svn_error_t *
  79 initialize_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  */
 158 svn_membuffer_t *
 159 svn_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
 176 void
 177 svn_cache_config_set(const svn_cache_config_t *settings)
 178 {
 179   cache_settings = *settings;
 180 }
 181