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-rw-r--r--libglusterfs/src/gidcache.c181
1 files changed, 181 insertions, 0 deletions
diff --git a/libglusterfs/src/gidcache.c b/libglusterfs/src/gidcache.c
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index 00000000000..9e508536d7e
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+++ b/libglusterfs/src/gidcache.c
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+/*
+ 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) {
+ gf_log("gid-cache", GF_LOG_DEBUG, "id %lu gl found - "
+ "bucket %d, index %d", id, bucket, i);
+ 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;
+
+ gf_log("gid-cache", GF_LOG_DEBUG, "id %lu gl added - bucket %d, index %d",
+ gl->gl_id, bucket, i);
+ UNLOCK(&cache->gc_lock);
+
+ return 1;
+}