diff options
Diffstat (limited to 'libglusterfs/src/gidcache.c')
| -rw-r--r-- | libglusterfs/src/gidcache.c | 177 |
1 files changed, 177 insertions, 0 deletions
diff --git a/libglusterfs/src/gidcache.c b/libglusterfs/src/gidcache.c new file mode 100644 index 00000000000..c55ed2581ba --- /dev/null +++ b/libglusterfs/src/gidcache.c @@ -0,0 +1,177 @@ +/* + Copyright (c) 2008-2012 Red Hat, Inc. <http://www.redhat.com> + This file is part of GlusterFS. + + This file is licensed to you under your choice of the GNU Lesser + General Public License, version 3 or any later version (LGPLv3 or + later), or the GNU General Public License, version 2 (GPLv2), in all + cases as published by the Free Software Foundation. +*/ + +#include "gidcache.h" +#include "mem-pool.h" + +/* + * We treat this as a very simple set-associative LRU cache, with entries aged + * out after a configurable interval. Hardly rocket science, but lots of + * details to worry about. + */ +#define BUCKET_START(p,n) ((p) + ((n) * AUX_GID_CACHE_ASSOC)) + +/* + * Initialize the cache. + */ +int gid_cache_init(gid_cache_t *cache, uint32_t timeout) +{ + if (!cache) + return -1; + + LOCK_INIT(&cache->gc_lock); + cache->gc_max_age = timeout; + cache->gc_nbuckets = AUX_GID_CACHE_BUCKETS; + memset(cache->gc_cache, 0, sizeof(gid_list_t) * AUX_GID_CACHE_SIZE); + + return 0; +} + +/* + * Look up an ID in the cache. If found, return the actual cache entry to avoid + * an additional allocation and memory copy. The caller should copy the data and + * release (unlock) the cache as soon as possible. + */ +const gid_list_t *gid_cache_lookup(gid_cache_t *cache, uint64_t id) +{ + int bucket; + int i; + time_t now; + const gid_list_t *agl; + + LOCK(&cache->gc_lock); + now = time(NULL); + bucket = id % cache->gc_nbuckets; + agl = BUCKET_START(cache->gc_cache, bucket); + for (i = 0; i < AUX_GID_CACHE_ASSOC; i++, agl++) { + if (!agl->gl_list) + continue; + if (agl->gl_id != id) + continue; + + /* + * We don't put new entries in the cache when expiration=0, but + * there might be entries still in there if expiration was + * changed very recently. Writing the check this way ensures + * that they're not used. + */ + if (now < agl->gl_deadline) { + return agl; + } + + /* + * We're not going to find any more UID matches, and reaping + * is handled further down to maintain LRU order. + */ + break; + } + UNLOCK(&cache->gc_lock); + return NULL; +} + +/* + * Release an entry found via lookup. + */ +void gid_cache_release(gid_cache_t *cache, const gid_list_t *agl) +{ + UNLOCK(&cache->gc_lock); +} + +/* + * Add a new list entry to the cache. If an entry for this ID already exists, + * update it. + */ +int gid_cache_add(gid_cache_t *cache, gid_list_t *gl) +{ + gid_list_t *agl; + int bucket; + int i; + time_t now; + + if (!gl || !gl->gl_list) + return -1; + + if (!cache->gc_max_age) + return 0; + + LOCK(&cache->gc_lock); + now = time(NULL); + + /* + * Scan for the first free entry or one that matches this id. The id + * check is added to address a bug where the cache might contain an + * expired entry for this id. Since lookup occurs in LRU order and + * does not reclaim entries, it will always return failure on discovery + * of an expired entry. This leads to duplicate entries being added, + * which still do not satisfy lookups until the expired entry (and + * everything before it) is reclaimed. + * + * We address this through reuse of an entry already allocated to this + * id, whether expired or not, since we have obviously already received + * more recent data. The entry is repopulated with the new data and a new + * deadline and is pushed forward to reside as the last populated entry in + * the bucket. + */ + bucket = gl->gl_id % cache->gc_nbuckets; + agl = BUCKET_START(cache->gc_cache, bucket); + for (i = 0; i < AUX_GID_CACHE_ASSOC; ++i, ++agl) { + if (agl->gl_id == gl->gl_id) + break; + if (!agl->gl_list) + break; + } + + /* + * The way we allocate free entries naturally places the newest + * ones at the highest indices, so evicting the lowest makes + * sense, but that also means we can't just replace it with the + * one that caused the eviction. That would cause us to thrash + * the first entry while others remain idle. Therefore, we + * need to slide the other entries down and add the new one at + * the end just as if the *last* slot had been free. + * + * Deadline expiration is also handled here, since the oldest + * expired entry will be in the first position. This does mean + * the bucket can stay full of expired entries if we're idle + * but, if the small amount of extra memory or scan time before + * we decide to evict someone ever become issues, we could + * easily add a reaper thread. + */ + + if (i >= AUX_GID_CACHE_ASSOC) { + /* cache full, evict the first (LRU) entry */ + i = 0; + agl = BUCKET_START(cache->gc_cache, bucket); + GF_FREE(agl->gl_list); + } else if (agl->gl_list) { + /* evict the old entry we plan to reuse */ + GF_FREE(agl->gl_list); + } + + /* + * If we have evicted an entry, slide the subsequent populated entries + * back and populate the last entry. + */ + for (; i < AUX_GID_CACHE_ASSOC - 1; i++) { + if (!agl[1].gl_list) + break; + agl[0] = agl[1]; + agl++; + } + + agl->gl_id = gl->gl_id; + agl->gl_count = gl->gl_count; + agl->gl_list = gl->gl_list; + agl->gl_deadline = now + cache->gc_max_age; + + UNLOCK(&cache->gc_lock); + + return 1; +} |