libglusterfs,mount/fuse: implement gidcache mechanism in fuse-bridge

This change genericizes the cache mechanism implemented in commit
8efd2845 into libglusterfs/src/gidcache.[ch] and adds fuse-bridge as
a client. The cache mechanism is fundamentally equivalent, with some
minor changes:

  - Change cache key from uid_t to uint64_t.
  - Modify the cache add logic to locate and use an entry with a
    matching ID, should it already exist. This addresses a bug in
    the existing mechanism where an expired entry supercedes a newly
    added entry in lookup, causing repeated adds and flushing of a
    cache bucket.

The fuse group cache is disabled by default. It can be enabled via
the 'gid-timeout' fuse-bridge translator option and accompanying
mount option (i.e., '-o gid-timeout=1' for a 1s entry timeout).

BUG: 800892
Change-Id: I0b34a2263ca48dbb154790a4a44fc70b733e9114
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-on: http://review.gluster.com/3676
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Reviewed-by: Anand Avati <avati@redhat.com>

1 files changed, 181 insertions, 0 deletions

diff --git a/libglusterfs/src/gidcache.c b/libglusterfs/src/gidcache.c
new file mode 100644
index 00000000000..9e508536d7e
--- /dev/null
+++ b/libglusterfs/src/gidcache.c
@@ -0,0 +1,181 @@
+/*
+  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;
+}