mbcache: Limit the maximum number of cache entries
Andreas Gruenbacher [Mon, 16 Aug 2010 17:05:23 +0000 (19:05 +0200)]
Limit the maximum number of mb_cache entries depending on the number of
hash buckets: if the only limit to the number of cache entries is the
available memory the hash chains can grow very long, taking a long time
to search.

At least partially solves https://bugzilla.lustre.org/show_bug.cgi?id=22771.

Signed-off-by: Andreas Gruenbacher <agruen@suse.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/mbcache.c

index cf4e6cd..9344474 100644 (file)
@@ -80,6 +80,7 @@ struct mb_cache {
        struct list_head                c_cache_list;
        const char                      *c_name;
        atomic_t                        c_entry_count;
+       int                             c_max_entries;
        int                             c_bucket_bits;
        struct kmem_cache               *c_entry_cache;
        struct list_head                *c_block_hash;
@@ -243,6 +244,12 @@ mb_cache_create(const char *name, int bucket_bits)
        if (!cache->c_entry_cache)
                goto fail2;
 
+       /*
+        * Set an upper limit on the number of cache entries so that the hash
+        * chains won't grow too long.
+        */
+       cache->c_max_entries = bucket_count << 4;
+
        spin_lock(&mb_cache_spinlock);
        list_add(&cache->c_cache_list, &mb_cache_list);
        spin_unlock(&mb_cache_spinlock);
@@ -333,7 +340,6 @@ mb_cache_destroy(struct mb_cache *cache)
        kfree(cache);
 }
 
-
 /*
  * mb_cache_entry_alloc()
  *
@@ -345,17 +351,29 @@ mb_cache_destroy(struct mb_cache *cache)
 struct mb_cache_entry *
 mb_cache_entry_alloc(struct mb_cache *cache, gfp_t gfp_flags)
 {
-       struct mb_cache_entry *ce;
-
-       ce = kmem_cache_alloc(cache->c_entry_cache, gfp_flags);
-       if (ce) {
+       struct mb_cache_entry *ce = NULL;
+
+       if (atomic_read(&cache->c_entry_count) >= cache->c_max_entries) {
+               spin_lock(&mb_cache_spinlock);
+               if (!list_empty(&mb_cache_lru_list)) {
+                       ce = list_entry(mb_cache_lru_list.next,
+                                       struct mb_cache_entry, e_lru_list);
+                       list_del_init(&ce->e_lru_list);
+                       __mb_cache_entry_unhash(ce);
+               }
+               spin_unlock(&mb_cache_spinlock);
+       }
+       if (!ce) {
+               ce = kmem_cache_alloc(cache->c_entry_cache, gfp_flags);
+               if (!ce)
+                       return NULL;
                atomic_inc(&cache->c_entry_count);
                INIT_LIST_HEAD(&ce->e_lru_list);
                INIT_LIST_HEAD(&ce->e_block_list);
                ce->e_cache = cache;
-               ce->e_used = 1 + MB_CACHE_WRITER;
                ce->e_queued = 0;
        }
+       ce->e_used = 1 + MB_CACHE_WRITER;
        return ce;
 }