1 // SPDX-License-Identifier: GPL-2.0-only
2 #include <linux/spinlock.h>
3 #include <linux/slab.h>
4 #include <linux/list.h>
5 #include <linux/list_bl.h>
6 #include <linux/module.h>
7 #include <linux/sched.h>
8 #include <linux/workqueue.h>
9 #include <linux/mbcache.h>
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
14 * mb_cache_entry_delete_or_get()).
16 * Ext2 and ext4 use this cache for deduplication of extended attribute blocks.
17 * Ext4 also uses it for deduplication of xattr values stored in inodes.
18 * They use hash of data as a key and provide a value that may represent a
19 * block or inode number. That's why keys need not be unique (hash of different
20 * data may be the same). However user provided value always uniquely
21 * identifies a cache entry.
23 * We provide functions for creation and removal of entries, search by key,
24 * and a special "delete entry with given key-value pair" operation. Fixed
25 * size hash table is used for fast key lookups.
29 /* Hash table of entries */
30 struct hlist_bl_head
*c_hash
;
31 /* log2 of hash table size */
33 /* Maximum entries in cache to avoid degrading hash too much */
34 unsigned long c_max_entries
;
35 /* Protects c_list, c_entry_count */
36 spinlock_t c_list_lock
;
37 struct list_head c_list
;
38 /* Number of entries in cache */
39 unsigned long c_entry_count
;
40 struct shrinker c_shrink
;
41 /* Work for shrinking when the cache has too many entries */
42 struct work_struct c_shrink_work
;
45 static struct kmem_cache
*mb_entry_cache
;
47 static unsigned long mb_cache_shrink(struct mb_cache
*cache
,
48 unsigned long nr_to_scan
);
50 static inline struct hlist_bl_head
*mb_cache_entry_head(struct mb_cache
*cache
,
53 return &cache
->c_hash
[hash_32(key
, cache
->c_bucket_bits
)];
57 * Number of entries to reclaim synchronously when there are too many entries
60 #define SYNC_SHRINK_BATCH 64
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.
72 * Otherwise 0 is returned.
74 int mb_cache_entry_create(struct mb_cache
*cache
, gfp_t mask
, u32 key
,
75 u64 value
, bool reusable
)
77 struct mb_cache_entry
*entry
, *dup
;
78 struct hlist_bl_node
*dup_node
;
79 struct hlist_bl_head
*head
;
81 /* Schedule background reclaim if there are too many entries */
82 if (cache
->c_entry_count
>= cache
->c_max_entries
)
83 schedule_work(&cache
->c_shrink_work
);
84 /* Do some sync reclaim if background reclaim cannot keep up */
85 if (cache
->c_entry_count
>= 2*cache
->c_max_entries
)
86 mb_cache_shrink(cache
, SYNC_SHRINK_BATCH
);
88 entry
= kmem_cache_alloc(mb_entry_cache
, mask
);
92 INIT_LIST_HEAD(&entry
->e_list
);
93 /* One ref for hash, one ref returned */
94 atomic_set(&entry
->e_refcnt
, 1);
96 entry
->e_value
= value
;
97 entry
->e_reusable
= reusable
;
98 entry
->e_referenced
= 0;
99 head
= mb_cache_entry_head(cache
, key
);
101 hlist_bl_for_each_entry(dup
, dup_node
, head
, e_hash_list
) {
102 if (dup
->e_key
== key
&& dup
->e_value
== value
) {
103 hlist_bl_unlock(head
);
104 kmem_cache_free(mb_entry_cache
, entry
);
108 hlist_bl_add_head(&entry
->e_hash_list
, head
);
109 hlist_bl_unlock(head
);
111 spin_lock(&cache
->c_list_lock
);
112 list_add_tail(&entry
->e_list
, &cache
->c_list
);
113 /* Grab ref for LRU list */
114 atomic_inc(&entry
->e_refcnt
);
115 cache
->c_entry_count
++;
116 spin_unlock(&cache
->c_list_lock
);
120 EXPORT_SYMBOL(mb_cache_entry_create
);
122 void __mb_cache_entry_free(struct mb_cache_entry
*entry
)
124 kmem_cache_free(mb_entry_cache
, entry
);
126 EXPORT_SYMBOL(__mb_cache_entry_free
);
129 * mb_cache_entry_wait_unused - wait to be the last user of the entry
131 * @entry - entry to work on
133 * Wait to be the last user of the entry.
135 void mb_cache_entry_wait_unused(struct mb_cache_entry
*entry
)
137 wait_var_event(&entry
->e_refcnt
, atomic_read(&entry
->e_refcnt
) <= 3);
139 EXPORT_SYMBOL(mb_cache_entry_wait_unused
);
141 static struct mb_cache_entry
*__entry_find(struct mb_cache
*cache
,
142 struct mb_cache_entry
*entry
,
145 struct mb_cache_entry
*old_entry
= entry
;
146 struct hlist_bl_node
*node
;
147 struct hlist_bl_head
*head
;
149 head
= mb_cache_entry_head(cache
, key
);
151 if (entry
&& !hlist_bl_unhashed(&entry
->e_hash_list
))
152 node
= entry
->e_hash_list
.next
;
154 node
= hlist_bl_first(head
);
156 entry
= hlist_bl_entry(node
, struct mb_cache_entry
,
158 if (entry
->e_key
== key
&& entry
->e_reusable
) {
159 atomic_inc(&entry
->e_refcnt
);
166 hlist_bl_unlock(head
);
168 mb_cache_entry_put(cache
, old_entry
);
174 * mb_cache_entry_find_first - find the first reusable entry with the given key
175 * @cache: cache where we should search
176 * @key: key to look for
178 * Search in @cache for a reusable entry with key @key. Grabs reference to the
179 * first reusable entry found and returns the entry.
181 struct mb_cache_entry
*mb_cache_entry_find_first(struct mb_cache
*cache
,
184 return __entry_find(cache
, NULL
, key
);
186 EXPORT_SYMBOL(mb_cache_entry_find_first
);
189 * mb_cache_entry_find_next - find next reusable entry with the same key
190 * @cache: cache where we should search
191 * @entry: entry to start search from
193 * Finds next reusable entry in the hash chain which has the same key as @entry.
194 * If @entry is unhashed (which can happen when deletion of entry races with the
195 * search), finds the first reusable entry in the hash chain. The function drops
196 * reference to @entry and returns with a reference to the found entry.
198 struct mb_cache_entry
*mb_cache_entry_find_next(struct mb_cache
*cache
,
199 struct mb_cache_entry
*entry
)
201 return __entry_find(cache
, entry
, entry
->e_key
);
203 EXPORT_SYMBOL(mb_cache_entry_find_next
);
206 * mb_cache_entry_get - get a cache entry by value (and key)
207 * @cache - cache we work with
211 struct mb_cache_entry
*mb_cache_entry_get(struct mb_cache
*cache
, u32 key
,
214 struct hlist_bl_node
*node
;
215 struct hlist_bl_head
*head
;
216 struct mb_cache_entry
*entry
;
218 head
= mb_cache_entry_head(cache
, key
);
220 hlist_bl_for_each_entry(entry
, node
, head
, e_hash_list
) {
221 if (entry
->e_key
== key
&& entry
->e_value
== value
) {
222 atomic_inc(&entry
->e_refcnt
);
228 hlist_bl_unlock(head
);
231 EXPORT_SYMBOL(mb_cache_entry_get
);
233 /* mb_cache_entry_delete - try to remove a cache entry
234 * @cache - cache we work with
238 * Remove entry from cache @cache with key @key and value @value.
240 void mb_cache_entry_delete(struct mb_cache
*cache
, u32 key
, u64 value
)
242 struct hlist_bl_node
*node
;
243 struct hlist_bl_head
*head
;
244 struct mb_cache_entry
*entry
;
246 head
= mb_cache_entry_head(cache
, key
);
248 hlist_bl_for_each_entry(entry
, node
, head
, e_hash_list
) {
249 if (entry
->e_key
== key
&& entry
->e_value
== value
) {
250 /* We keep hash list reference to keep entry alive */
251 hlist_bl_del_init(&entry
->e_hash_list
);
252 hlist_bl_unlock(head
);
253 spin_lock(&cache
->c_list_lock
);
254 if (!list_empty(&entry
->e_list
)) {
255 list_del_init(&entry
->e_list
);
256 if (!WARN_ONCE(cache
->c_entry_count
== 0,
257 "mbcache: attempt to decrement c_entry_count past zero"))
258 cache
->c_entry_count
--;
259 atomic_dec(&entry
->e_refcnt
);
261 spin_unlock(&cache
->c_list_lock
);
262 mb_cache_entry_put(cache
, entry
);
266 hlist_bl_unlock(head
);
268 EXPORT_SYMBOL(mb_cache_entry_delete
);
270 /* mb_cache_entry_delete_or_get - remove a cache entry if it has no users
271 * @cache - cache we work with
275 * Remove entry from cache @cache with key @key and value @value. The removal
276 * happens only if the entry is unused. The function returns NULL in case the
277 * entry was successfully removed or there's no entry in cache. Otherwise the
278 * function grabs reference of the entry that we failed to delete because it
279 * still has users and return it.
281 struct mb_cache_entry
*mb_cache_entry_delete_or_get(struct mb_cache
*cache
,
284 struct hlist_bl_node
*node
;
285 struct hlist_bl_head
*head
;
286 struct mb_cache_entry
*entry
;
288 head
= mb_cache_entry_head(cache
, key
);
290 hlist_bl_for_each_entry(entry
, node
, head
, e_hash_list
) {
291 if (entry
->e_key
== key
&& entry
->e_value
== value
) {
292 if (atomic_read(&entry
->e_refcnt
) > 2) {
293 atomic_inc(&entry
->e_refcnt
);
294 hlist_bl_unlock(head
);
297 /* We keep hash list reference to keep entry alive */
298 hlist_bl_del_init(&entry
->e_hash_list
);
299 hlist_bl_unlock(head
);
300 spin_lock(&cache
->c_list_lock
);
301 if (!list_empty(&entry
->e_list
)) {
302 list_del_init(&entry
->e_list
);
303 if (!WARN_ONCE(cache
->c_entry_count
== 0,
304 "mbcache: attempt to decrement c_entry_count past zero"))
305 cache
->c_entry_count
--;
306 atomic_dec(&entry
->e_refcnt
);
308 spin_unlock(&cache
->c_list_lock
);
309 mb_cache_entry_put(cache
, entry
);
313 hlist_bl_unlock(head
);
317 EXPORT_SYMBOL(mb_cache_entry_delete_or_get
);
319 /* mb_cache_entry_touch - cache entry got used
320 * @cache - cache the entry belongs to
321 * @entry - entry that got used
323 * Marks entry as used to give hit higher chances of surviving in cache.
325 void mb_cache_entry_touch(struct mb_cache
*cache
,
326 struct mb_cache_entry
*entry
)
328 entry
->e_referenced
= 1;
330 EXPORT_SYMBOL(mb_cache_entry_touch
);
332 static unsigned long mb_cache_count(struct shrinker
*shrink
,
333 struct shrink_control
*sc
)
335 struct mb_cache
*cache
= container_of(shrink
, struct mb_cache
,
338 return cache
->c_entry_count
;
341 /* Shrink number of entries in cache */
342 static unsigned long mb_cache_shrink(struct mb_cache
*cache
,
343 unsigned long nr_to_scan
)
345 struct mb_cache_entry
*entry
;
346 struct hlist_bl_head
*head
;
347 unsigned long shrunk
= 0;
349 spin_lock(&cache
->c_list_lock
);
350 while (nr_to_scan
-- && !list_empty(&cache
->c_list
)) {
351 entry
= list_first_entry(&cache
->c_list
,
352 struct mb_cache_entry
, e_list
);
353 if (entry
->e_referenced
|| atomic_read(&entry
->e_refcnt
) > 2) {
354 entry
->e_referenced
= 0;
355 list_move_tail(&entry
->e_list
, &cache
->c_list
);
358 list_del_init(&entry
->e_list
);
359 cache
->c_entry_count
--;
361 * We keep LRU list reference so that entry doesn't go away
364 spin_unlock(&cache
->c_list_lock
);
365 head
= mb_cache_entry_head(cache
, entry
->e_key
);
367 /* Now a reliable check if the entry didn't get used... */
368 if (atomic_read(&entry
->e_refcnt
) > 2) {
369 hlist_bl_unlock(head
);
370 spin_lock(&cache
->c_list_lock
);
371 list_add_tail(&entry
->e_list
, &cache
->c_list
);
372 cache
->c_entry_count
++;
375 if (!hlist_bl_unhashed(&entry
->e_hash_list
)) {
376 hlist_bl_del_init(&entry
->e_hash_list
);
377 atomic_dec(&entry
->e_refcnt
);
379 hlist_bl_unlock(head
);
380 if (mb_cache_entry_put(cache
, entry
))
383 spin_lock(&cache
->c_list_lock
);
385 spin_unlock(&cache
->c_list_lock
);
390 static unsigned long mb_cache_scan(struct shrinker
*shrink
,
391 struct shrink_control
*sc
)
393 struct mb_cache
*cache
= container_of(shrink
, struct mb_cache
,
395 return mb_cache_shrink(cache
, sc
->nr_to_scan
);
398 /* We shrink 1/X of the cache when we have too many entries in it */
399 #define SHRINK_DIVISOR 16
401 static void mb_cache_shrink_worker(struct work_struct
*work
)
403 struct mb_cache
*cache
= container_of(work
, struct mb_cache
,
405 mb_cache_shrink(cache
, cache
->c_max_entries
/ SHRINK_DIVISOR
);
409 * mb_cache_create - create cache
410 * @bucket_bits: log2 of the hash table size
412 * Create cache for keys with 2^bucket_bits hash entries.
414 struct mb_cache
*mb_cache_create(int bucket_bits
)
416 struct mb_cache
*cache
;
417 unsigned long bucket_count
= 1UL << bucket_bits
;
420 cache
= kzalloc(sizeof(struct mb_cache
), GFP_KERNEL
);
423 cache
->c_bucket_bits
= bucket_bits
;
424 cache
->c_max_entries
= bucket_count
<< 4;
425 INIT_LIST_HEAD(&cache
->c_list
);
426 spin_lock_init(&cache
->c_list_lock
);
427 cache
->c_hash
= kmalloc_array(bucket_count
,
428 sizeof(struct hlist_bl_head
),
430 if (!cache
->c_hash
) {
434 for (i
= 0; i
< bucket_count
; i
++)
435 INIT_HLIST_BL_HEAD(&cache
->c_hash
[i
]);
437 cache
->c_shrink
.count_objects
= mb_cache_count
;
438 cache
->c_shrink
.scan_objects
= mb_cache_scan
;
439 cache
->c_shrink
.seeks
= DEFAULT_SEEKS
;
440 if (register_shrinker(&cache
->c_shrink
)) {
441 kfree(cache
->c_hash
);
446 INIT_WORK(&cache
->c_shrink_work
, mb_cache_shrink_worker
);
453 EXPORT_SYMBOL(mb_cache_create
);
456 * mb_cache_destroy - destroy cache
457 * @cache: the cache to destroy
459 * Free all entries in cache and cache itself. Caller must make sure nobody
460 * (except shrinker) can reach @cache when calling this.
462 void mb_cache_destroy(struct mb_cache
*cache
)
464 struct mb_cache_entry
*entry
, *next
;
466 unregister_shrinker(&cache
->c_shrink
);
469 * We don't bother with any locking. Cache must not be used at this
472 list_for_each_entry_safe(entry
, next
, &cache
->c_list
, e_list
) {
473 if (!hlist_bl_unhashed(&entry
->e_hash_list
)) {
474 hlist_bl_del_init(&entry
->e_hash_list
);
475 atomic_dec(&entry
->e_refcnt
);
478 list_del(&entry
->e_list
);
479 WARN_ON(atomic_read(&entry
->e_refcnt
) != 1);
480 mb_cache_entry_put(cache
, entry
);
482 kfree(cache
->c_hash
);
485 EXPORT_SYMBOL(mb_cache_destroy
);
487 static int __init
mbcache_init(void)
489 mb_entry_cache
= kmem_cache_create("mbcache",
490 sizeof(struct mb_cache_entry
), 0,
491 SLAB_RECLAIM_ACCOUNT
|SLAB_MEM_SPREAD
, NULL
);
497 static void __exit
mbcache_exit(void)
499 kmem_cache_destroy(mb_entry_cache
);
502 module_init(mbcache_init
)
503 module_exit(mbcache_exit
)
505 MODULE_AUTHOR("Jan Kara <jack@suse.cz>");
506 MODULE_DESCRIPTION("Meta block cache (for extended attributes)");
507 MODULE_LICENSE("GPL");