1 #include <linux/spinlock.h>
2 #include <linux/slab.h>
3 #include <linux/list.h>
4 #include <linux/list_bl.h>
5 #include <linux/module.h>
6 #include <linux/sched.h>
7 #include <linux/workqueue.h>
8 #include <linux/mbcache.h>
11 * Mbcache is a simple key-value store. Keys need not be unique, however
12 * key-value pairs are expected to be unique (we use this fact in
13 * mb_cache_entry_delete_block()).
15 * Ext2 and ext4 use this cache for deduplication of extended attribute blocks.
16 * They use hash of a block contents as a key and block number as a value.
17 * That's why keys need not be unique (different xattr blocks may end up having
18 * the same hash). However block number always uniquely identifies a cache
21 * We provide functions for creation and removal of entries, search by key,
22 * and a special "delete entry with given key-value pair" operation. Fixed
23 * size hash table is used for fast key lookups.
27 /* Hash table of entries */
28 struct hlist_bl_head *c_hash;
29 /* log2 of hash table size */
31 /* Maximum entries in cache to avoid degrading hash too much */
33 /* Protects c_list, c_entry_count */
34 spinlock_t c_list_lock;
35 struct list_head c_list;
36 /* Number of entries in cache */
37 unsigned long c_entry_count;
38 struct shrinker c_shrink;
39 /* Work for shrinking when the cache has too many entries */
40 struct work_struct c_shrink_work;
43 static struct kmem_cache *mb_entry_cache;
45 static unsigned long mb_cache_shrink(struct mb_cache *cache,
46 unsigned int nr_to_scan);
48 static inline struct hlist_bl_head *mb_cache_entry_head(struct mb_cache *cache,
51 return &cache->c_hash[hash_32(key, cache->c_bucket_bits)];
55 * Number of entries to reclaim synchronously when there are too many entries
58 #define SYNC_SHRINK_BATCH 64
61 * mb_cache_entry_create - create entry in cache
62 * @cache - cache where the entry should be created
63 * @mask - gfp mask with which the entry should be allocated
64 * @key - key of the entry
65 * @block - block that contains data
66 * @reusable - is the block reusable by other inodes?
68 * Creates entry in @cache with key @key and records that data is stored in
69 * block @block. The function returns -EBUSY if entry with the same key
70 * and for the same block already exists in cache. Otherwise 0 is returned.
72 int mb_cache_entry_create(struct mb_cache *cache, gfp_t mask, u32 key,
73 sector_t block, bool reusable)
75 struct mb_cache_entry *entry, *dup;
76 struct hlist_bl_node *dup_node;
77 struct hlist_bl_head *head;
79 /* Schedule background reclaim if there are too many entries */
80 if (cache->c_entry_count >= cache->c_max_entries)
81 schedule_work(&cache->c_shrink_work);
82 /* Do some sync reclaim if background reclaim cannot keep up */
83 if (cache->c_entry_count >= 2*cache->c_max_entries)
84 mb_cache_shrink(cache, SYNC_SHRINK_BATCH);
86 entry = kmem_cache_alloc(mb_entry_cache, mask);
90 INIT_LIST_HEAD(&entry->e_list);
91 /* One ref for hash, one ref returned */
92 atomic_set(&entry->e_refcnt, 1);
94 entry->e_block = block;
95 entry->e_reusable = reusable;
96 head = mb_cache_entry_head(cache, key);
98 hlist_bl_for_each_entry(dup, dup_node, head, e_hash_list) {
99 if (dup->e_key == key && dup->e_block == block) {
100 hlist_bl_unlock(head);
101 kmem_cache_free(mb_entry_cache, entry);
105 hlist_bl_add_head(&entry->e_hash_list, head);
106 hlist_bl_unlock(head);
108 spin_lock(&cache->c_list_lock);
109 list_add_tail(&entry->e_list, &cache->c_list);
110 /* Grab ref for LRU list */
111 atomic_inc(&entry->e_refcnt);
112 cache->c_entry_count++;
113 spin_unlock(&cache->c_list_lock);
117 EXPORT_SYMBOL(mb_cache_entry_create);
119 void __mb_cache_entry_free(struct mb_cache_entry *entry)
121 kmem_cache_free(mb_entry_cache, entry);
123 EXPORT_SYMBOL(__mb_cache_entry_free);
125 static struct mb_cache_entry *__entry_find(struct mb_cache *cache,
126 struct mb_cache_entry *entry,
129 struct mb_cache_entry *old_entry = entry;
130 struct hlist_bl_node *node;
131 struct hlist_bl_head *head;
133 head = mb_cache_entry_head(cache, key);
135 if (entry && !hlist_bl_unhashed(&entry->e_hash_list))
136 node = entry->e_hash_list.next;
138 node = hlist_bl_first(head);
140 entry = hlist_bl_entry(node, struct mb_cache_entry,
142 if (entry->e_key == key && entry->e_reusable) {
143 atomic_inc(&entry->e_refcnt);
150 hlist_bl_unlock(head);
152 mb_cache_entry_put(cache, old_entry);
158 * mb_cache_entry_find_first - find the first entry in cache with given key
159 * @cache: cache where we should search
160 * @key: key to look for
162 * Search in @cache for entry with key @key. Grabs reference to the first
163 * entry found and returns the entry.
165 struct mb_cache_entry *mb_cache_entry_find_first(struct mb_cache *cache,
168 return __entry_find(cache, NULL, key);
170 EXPORT_SYMBOL(mb_cache_entry_find_first);
173 * mb_cache_entry_find_next - find next entry in cache with the same
174 * @cache: cache where we should search
175 * @entry: entry to start search from
177 * Finds next entry in the hash chain which has the same key as @entry.
178 * If @entry is unhashed (which can happen when deletion of entry races
179 * with the search), finds the first entry in the hash chain. The function
180 * drops reference to @entry and returns with a reference to the found entry.
182 struct mb_cache_entry *mb_cache_entry_find_next(struct mb_cache *cache,
183 struct mb_cache_entry *entry)
185 return __entry_find(cache, entry, entry->e_key);
187 EXPORT_SYMBOL(mb_cache_entry_find_next);
190 * mb_cache_entry_get - get a cache entry by block number (and key)
191 * @cache - cache we work with
192 * @key - key of block number @block
193 * @block - block number
195 struct mb_cache_entry *mb_cache_entry_get(struct mb_cache *cache, u32 key,
198 struct hlist_bl_node *node;
199 struct hlist_bl_head *head;
200 struct mb_cache_entry *entry;
202 head = mb_cache_entry_head(cache, key);
204 hlist_bl_for_each_entry(entry, node, head, e_hash_list) {
205 if (entry->e_key == key && entry->e_block == block) {
206 atomic_inc(&entry->e_refcnt);
212 hlist_bl_unlock(head);
215 EXPORT_SYMBOL(mb_cache_entry_get);
217 /* mb_cache_entry_delete_block - remove information about block from cache
218 * @cache - cache we work with
219 * @key - key of block @block
220 * @block - block number
222 * Remove entry from cache @cache with key @key with data stored in @block.
224 void mb_cache_entry_delete_block(struct mb_cache *cache, u32 key,
227 struct hlist_bl_node *node;
228 struct hlist_bl_head *head;
229 struct mb_cache_entry *entry;
231 head = mb_cache_entry_head(cache, key);
233 hlist_bl_for_each_entry(entry, node, head, e_hash_list) {
234 if (entry->e_key == key && entry->e_block == block) {
235 /* We keep hash list reference to keep entry alive */
236 hlist_bl_del_init(&entry->e_hash_list);
237 hlist_bl_unlock(head);
238 spin_lock(&cache->c_list_lock);
239 if (!list_empty(&entry->e_list)) {
240 list_del_init(&entry->e_list);
241 cache->c_entry_count--;
242 atomic_dec(&entry->e_refcnt);
244 spin_unlock(&cache->c_list_lock);
245 mb_cache_entry_put(cache, entry);
249 hlist_bl_unlock(head);
251 EXPORT_SYMBOL(mb_cache_entry_delete_block);
253 /* mb_cache_entry_touch - cache entry got used
254 * @cache - cache the entry belongs to
255 * @entry - entry that got used
257 * Marks entry as used to give hit higher chances of surviving in cache.
259 void mb_cache_entry_touch(struct mb_cache *cache,
260 struct mb_cache_entry *entry)
262 entry->e_referenced = 1;
264 EXPORT_SYMBOL(mb_cache_entry_touch);
266 static unsigned long mb_cache_count(struct shrinker *shrink,
267 struct shrink_control *sc)
269 struct mb_cache *cache = container_of(shrink, struct mb_cache,
272 return cache->c_entry_count;
275 /* Shrink number of entries in cache */
276 static unsigned long mb_cache_shrink(struct mb_cache *cache,
277 unsigned int nr_to_scan)
279 struct mb_cache_entry *entry;
280 struct hlist_bl_head *head;
281 unsigned int shrunk = 0;
283 spin_lock(&cache->c_list_lock);
284 while (nr_to_scan-- && !list_empty(&cache->c_list)) {
285 entry = list_first_entry(&cache->c_list,
286 struct mb_cache_entry, e_list);
287 if (entry->e_referenced) {
288 entry->e_referenced = 0;
289 list_move_tail(&cache->c_list, &entry->e_list);
292 list_del_init(&entry->e_list);
293 cache->c_entry_count--;
295 * We keep LRU list reference so that entry doesn't go away
298 spin_unlock(&cache->c_list_lock);
299 head = mb_cache_entry_head(cache, entry->e_key);
301 if (!hlist_bl_unhashed(&entry->e_hash_list)) {
302 hlist_bl_del_init(&entry->e_hash_list);
303 atomic_dec(&entry->e_refcnt);
305 hlist_bl_unlock(head);
306 if (mb_cache_entry_put(cache, entry))
309 spin_lock(&cache->c_list_lock);
311 spin_unlock(&cache->c_list_lock);
316 static unsigned long mb_cache_scan(struct shrinker *shrink,
317 struct shrink_control *sc)
319 int nr_to_scan = sc->nr_to_scan;
320 struct mb_cache *cache = container_of(shrink, struct mb_cache,
322 return mb_cache_shrink(cache, nr_to_scan);
325 /* We shrink 1/X of the cache when we have too many entries in it */
326 #define SHRINK_DIVISOR 16
328 static void mb_cache_shrink_worker(struct work_struct *work)
330 struct mb_cache *cache = container_of(work, struct mb_cache,
332 mb_cache_shrink(cache, cache->c_max_entries / SHRINK_DIVISOR);
336 * mb_cache_create - create cache
337 * @bucket_bits: log2 of the hash table size
339 * Create cache for keys with 2^bucket_bits hash entries.
341 struct mb_cache *mb_cache_create(int bucket_bits)
343 struct mb_cache *cache;
344 int bucket_count = 1 << bucket_bits;
347 if (!try_module_get(THIS_MODULE))
350 cache = kzalloc(sizeof(struct mb_cache), GFP_KERNEL);
353 cache->c_bucket_bits = bucket_bits;
354 cache->c_max_entries = bucket_count << 4;
355 INIT_LIST_HEAD(&cache->c_list);
356 spin_lock_init(&cache->c_list_lock);
357 cache->c_hash = kmalloc(bucket_count * sizeof(struct hlist_bl_head),
359 if (!cache->c_hash) {
363 for (i = 0; i < bucket_count; i++)
364 INIT_HLIST_BL_HEAD(&cache->c_hash[i]);
366 cache->c_shrink.count_objects = mb_cache_count;
367 cache->c_shrink.scan_objects = mb_cache_scan;
368 cache->c_shrink.seeks = DEFAULT_SEEKS;
369 register_shrinker(&cache->c_shrink);
371 INIT_WORK(&cache->c_shrink_work, mb_cache_shrink_worker);
376 module_put(THIS_MODULE);
379 EXPORT_SYMBOL(mb_cache_create);
382 * mb_cache_destroy - destroy cache
383 * @cache: the cache to destroy
385 * Free all entries in cache and cache itself. Caller must make sure nobody
386 * (except shrinker) can reach @cache when calling this.
388 void mb_cache_destroy(struct mb_cache *cache)
390 struct mb_cache_entry *entry, *next;
392 unregister_shrinker(&cache->c_shrink);
395 * We don't bother with any locking. Cache must not be used at this
398 list_for_each_entry_safe(entry, next, &cache->c_list, e_list) {
399 if (!hlist_bl_unhashed(&entry->e_hash_list)) {
400 hlist_bl_del_init(&entry->e_hash_list);
401 atomic_dec(&entry->e_refcnt);
404 list_del(&entry->e_list);
405 WARN_ON(atomic_read(&entry->e_refcnt) != 1);
406 mb_cache_entry_put(cache, entry);
408 kfree(cache->c_hash);
410 module_put(THIS_MODULE);
412 EXPORT_SYMBOL(mb_cache_destroy);
414 static int __init mbcache_init(void)
416 mb_entry_cache = kmem_cache_create("mbcache",
417 sizeof(struct mb_cache_entry), 0,
418 SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL);
419 BUG_ON(!mb_entry_cache);
423 static void __exit mbcache_exit(void)
425 kmem_cache_destroy(mb_entry_cache);
428 module_init(mbcache_init)
429 module_exit(mbcache_exit)
431 MODULE_AUTHOR("Jan Kara <jack@suse.cz>");
432 MODULE_DESCRIPTION("Meta block cache (for extended attributes)");
433 MODULE_LICENSE("GPL");