1 // SPDX-License-Identifier: GPL-2.0-only
12  * Mbcache is a simple key-value store. Keys need not be unique, however
13  * key-value pairs are expected to be unique (we use this fact in
16  * Ext2 and ext4 use this cache for deduplication of extended attribute blocks.
21  * identifies a cache entry.
24  * and a special "delete entry with given key-value pair" operation. Fixed
33 	/* Maximum entries in cache to avoid degrading hash too much */
38 	/* Number of entries in cache */
41 	/* Work for shrinking when the cache has too many entries */
47 static unsigned long mb_cache_shrink(struct mb_cache *cache,
50 static inline struct hlist_bl_head *mb_cache_entry_head(struct mb_cache *cache,  in mb_cache_entry_head()  argument
53 	return &cache->c_hash[hash_32(key, cache->c_bucket_bits)];  in mb_cache_entry_head()
58  * in cache
63  * mb_cache_entry_create - create entry in cache
64  * @cache - cache where the entry should be created
65  * @mask - gfp mask with which the entry should be allocated
66  * @key - key of the entry
67  * @value - value of the entry
68  * @reusable - is the entry reusable by others?
70  * Creates entry in @cache with key @key and value @value. The function returns
71  * -EBUSY if entry with the same key and value already exists in cache.
74 int mb_cache_entry_create(struct mb_cache *cache, gfp_t mask, u32 key,  in mb_cache_entry_create()  argument
82 	if (cache->c_entry_count >= cache->c_max_entries)  in mb_cache_entry_create()
83 		schedule_work(&cache->c_shrink_work);  in mb_cache_entry_create()
85 	if (cache->c_entry_count >= 2*cache->c_max_entries)  in mb_cache_entry_create()
86 		mb_cache_shrink(cache, SYNC_SHRINK_BATCH);  in mb_cache_entry_create()
90 		return -ENOMEM;  in mb_cache_entry_create()
92 	INIT_LIST_HEAD(&entry->e_list);  in mb_cache_entry_create()
97 	 * avoids nesting of cache->c_list_lock into hash table bit locks which  in mb_cache_entry_create()
100 	atomic_set(&entry->e_refcnt, 2);  in mb_cache_entry_create()
101 	entry->e_key = key;  in mb_cache_entry_create()
102 	entry->e_value = value;  in mb_cache_entry_create()
103 	entry->e_flags = 0;  in mb_cache_entry_create()
105 		set_bit(MBE_REUSABLE_B, &entry->e_flags);  in mb_cache_entry_create()
106 	head = mb_cache_entry_head(cache, key);  in mb_cache_entry_create()
109 		if (dup->e_key == key && dup->e_value == value) {  in mb_cache_entry_create()
112 			return -EBUSY;  in mb_cache_entry_create()
115 	hlist_bl_add_head(&entry->e_hash_list, head);  in mb_cache_entry_create()
117 	spin_lock(&cache->c_list_lock);  in mb_cache_entry_create()
118 	list_add_tail(&entry->e_list, &cache->c_list);  in mb_cache_entry_create()
119 	cache->c_entry_count++;  in mb_cache_entry_create()
120 	spin_unlock(&cache->c_list_lock);  in mb_cache_entry_create()
121 	mb_cache_entry_put(cache, entry);  in mb_cache_entry_create()
127 void __mb_cache_entry_free(struct mb_cache *cache, struct mb_cache_entry *entry)  in __mb_cache_entry_free()  argument
131 	head = mb_cache_entry_head(cache, entry->e_key);  in __mb_cache_entry_free()
133 	hlist_bl_del(&entry->e_hash_list);  in __mb_cache_entry_free()
140  * mb_cache_entry_wait_unused - wait to be the last user of the entry
142  * @entry - entry to work on
148 	wait_var_event(&entry->e_refcnt, atomic_read(&entry->e_refcnt) <= 2);  in mb_cache_entry_wait_unused()
152 static struct mb_cache_entry *__entry_find(struct mb_cache *cache,  in __entry_find()  argument
160 	head = mb_cache_entry_head(cache, key);  in __entry_find()
162 	if (entry && !hlist_bl_unhashed(&entry->e_hash_list))  in __entry_find()
163 		node = entry->e_hash_list.next;  in __entry_find()
169 		if (entry->e_key == key &&  in __entry_find()
170 		    test_bit(MBE_REUSABLE_B, &entry->e_flags) &&  in __entry_find()
171 		    atomic_inc_not_zero(&entry->e_refcnt))  in __entry_find()
173 		node = node->next;  in __entry_find()
179 		mb_cache_entry_put(cache, old_entry);  in __entry_find()
185  * mb_cache_entry_find_first - find the first reusable entry with the given key
186  * @cache: cache where we should search
189  * Search in @cache for a reusable entry with key @key. Grabs reference to the
192 struct mb_cache_entry *mb_cache_entry_find_first(struct mb_cache *cache,  in mb_cache_entry_find_first()  argument
195 	return __entry_find(cache, NULL, key);  in mb_cache_entry_find_first()
200  * mb_cache_entry_find_next - find next reusable entry with the same key
201  * @cache: cache where we should search
209 struct mb_cache_entry *mb_cache_entry_find_next(struct mb_cache *cache,  in mb_cache_entry_find_next()  argument
212 	return __entry_find(cache, entry, entry->e_key);  in mb_cache_entry_find_next()
217  * mb_cache_entry_get - get a cache entry by value (and key)
218  * @cache - cache we work with
219  * @key - key
220  * @value - value
222 struct mb_cache_entry *mb_cache_entry_get(struct mb_cache *cache, u32 key,  in mb_cache_entry_get()  argument
229 	head = mb_cache_entry_head(cache, key);  in mb_cache_entry_get()
232 		if (entry->e_key == key && entry->e_value == value &&  in mb_cache_entry_get()
233 		    atomic_inc_not_zero(&entry->e_refcnt))  in mb_cache_entry_get()
243 /* mb_cache_entry_delete_or_get - remove a cache entry if it has no users
244  * @cache - cache we work with
245  * @key - key
246  * @value - value
248  * Remove entry from cache @cache with key @key and value @value. The removal
250  * entry was successfully removed or there's no entry in cache. Otherwise the
254 struct mb_cache_entry *mb_cache_entry_delete_or_get(struct mb_cache *cache,  in mb_cache_entry_delete_or_get()  argument
259 	entry = mb_cache_entry_get(cache, key, value);  in mb_cache_entry_delete_or_get()
267 	if (atomic_cmpxchg(&entry->e_refcnt, 2, 0) != 2)  in mb_cache_entry_delete_or_get()
270 	spin_lock(&cache->c_list_lock);  in mb_cache_entry_delete_or_get()
271 	if (!list_empty(&entry->e_list))  in mb_cache_entry_delete_or_get()
272 		list_del_init(&entry->e_list);  in mb_cache_entry_delete_or_get()
273 	cache->c_entry_count--;  in mb_cache_entry_delete_or_get()
274 	spin_unlock(&cache->c_list_lock);  in mb_cache_entry_delete_or_get()
275 	__mb_cache_entry_free(cache, entry);  in mb_cache_entry_delete_or_get()
280 /* mb_cache_entry_touch - cache entry got used
281  * @cache - cache the entry belongs to
282  * @entry - entry that got used
284  * Marks entry as used to give hit higher chances of surviving in cache.
286 void mb_cache_entry_touch(struct mb_cache *cache,  in mb_cache_entry_touch()  argument
289 	set_bit(MBE_REFERENCED_B, &entry->e_flags);  in mb_cache_entry_touch()
296 	struct mb_cache *cache = shrink->private_data;  in mb_cache_count()  local
298 	return cache->c_entry_count;  in mb_cache_count()
301 /* Shrink number of entries in cache */
302 static unsigned long mb_cache_shrink(struct mb_cache *cache,  in mb_cache_shrink()  argument
308 	spin_lock(&cache->c_list_lock);  in mb_cache_shrink()
309 	while (nr_to_scan-- && !list_empty(&cache->c_list)) {  in mb_cache_shrink()
310 		entry = list_first_entry(&cache->c_list,  in mb_cache_shrink()
313 		if (test_bit(MBE_REFERENCED_B, &entry->e_flags) ||  in mb_cache_shrink()
314 		    atomic_cmpxchg(&entry->e_refcnt, 1, 0) != 1) {  in mb_cache_shrink()
315 			clear_bit(MBE_REFERENCED_B, &entry->e_flags);  in mb_cache_shrink()
316 			list_move_tail(&entry->e_list, &cache->c_list);  in mb_cache_shrink()
319 		list_del_init(&entry->e_list);  in mb_cache_shrink()
320 		cache->c_entry_count--;  in mb_cache_shrink()
321 		spin_unlock(&cache->c_list_lock);  in mb_cache_shrink()
322 		__mb_cache_entry_free(cache, entry);  in mb_cache_shrink()
325 		spin_lock(&cache->c_list_lock);  in mb_cache_shrink()
327 	spin_unlock(&cache->c_list_lock);  in mb_cache_shrink()
335 	struct mb_cache *cache = shrink->private_data;  in mb_cache_scan()  local
336 	return mb_cache_shrink(cache, sc->nr_to_scan);  in mb_cache_scan()
339 /* We shrink 1/X of the cache when we have too many entries in it */
344 	struct mb_cache *cache = container_of(work, struct mb_cache,  in mb_cache_shrink_worker()  local
346 	mb_cache_shrink(cache, cache->c_max_entries / SHRINK_DIVISOR);  in mb_cache_shrink_worker()
350  * mb_cache_create - create cache
353  * Create cache for keys with 2^bucket_bits hash entries.
357 	struct mb_cache *cache;  in mb_cache_create()  local
361 	cache = kzalloc(sizeof(struct mb_cache), GFP_KERNEL);  in mb_cache_create()
362 	if (!cache)  in mb_cache_create()
364 	cache->c_bucket_bits = bucket_bits;  in mb_cache_create()
365 	cache->c_max_entries = bucket_count << 4;  in mb_cache_create()
366 	INIT_LIST_HEAD(&cache->c_list);  in mb_cache_create()
367 	spin_lock_init(&cache->c_list_lock);  in mb_cache_create()
368 	cache->c_hash = kmalloc_array(bucket_count,  in mb_cache_create()
371 	if (!cache->c_hash) {  in mb_cache_create()
372 		kfree(cache);  in mb_cache_create()
376 		INIT_HLIST_BL_HEAD(&cache->c_hash[i]);  in mb_cache_create()
378 	cache->c_shrink = shrinker_alloc(0, "mbcache-shrinker");  in mb_cache_create()
379 	if (!cache->c_shrink) {  in mb_cache_create()
380 		kfree(cache->c_hash);  in mb_cache_create()
381 		kfree(cache);  in mb_cache_create()
385 	cache->c_shrink->count_objects = mb_cache_count;  in mb_cache_create()
386 	cache->c_shrink->scan_objects = mb_cache_scan;  in mb_cache_create()
387 	cache->c_shrink->private_data = cache;  in mb_cache_create()
389 	shrinker_register(cache->c_shrink);  in mb_cache_create()
391 	INIT_WORK(&cache->c_shrink_work, mb_cache_shrink_worker);  in mb_cache_create()
393 	return cache;  in mb_cache_create()
401  * mb_cache_destroy - destroy cache
402  * @cache: the cache to destroy
404  * Free all entries in cache and cache itself. Caller must make sure nobody
405  * (except shrinker) can reach @cache when calling this.
407 void mb_cache_destroy(struct mb_cache *cache)  in mb_cache_destroy()  argument
411 	shrinker_free(cache->c_shrink);  in mb_cache_destroy()
414 	 * We don't bother with any locking. Cache must not be used at this  in mb_cache_destroy()
417 	list_for_each_entry_safe(entry, next, &cache->c_list, e_list) {  in mb_cache_destroy()
418 		list_del(&entry->e_list);  in mb_cache_destroy()
419 		WARN_ON(atomic_read(&entry->e_refcnt) != 1);  in mb_cache_destroy()
420 		mb_cache_entry_put(cache, entry);  in mb_cache_destroy()
422 	kfree(cache->c_hash);  in mb_cache_destroy()
423 	kfree(cache);  in mb_cache_destroy()
431 		return -ENOMEM;  in mbcache_init()
444 MODULE_DESCRIPTION("Meta block cache (for extended attributes)");