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path: root/fs/mbcache.c (plain)
blob: 27e6bf6f09c6333f6fc790f2cdef9335c059c3bd
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>
9
10/*
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()).
14 *
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
19 * entry.
20 *
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.
24 */
25
26struct mb_cache {
27 /* Hash table of entries */
28 struct hlist_bl_head *c_hash;
29 /* log2 of hash table size */
30 int c_bucket_bits;
31 /* Maximum entries in cache to avoid degrading hash too much */
32 int c_max_entries;
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;
41};
42
43static struct kmem_cache *mb_entry_cache;
44
45static unsigned long mb_cache_shrink(struct mb_cache *cache,
46 unsigned int nr_to_scan);
47
48static inline struct hlist_bl_head *mb_cache_entry_head(struct mb_cache *cache,
49 u32 key)
50{
51 return &cache->c_hash[hash_32(key, cache->c_bucket_bits)];
52}
53
54/*
55 * Number of entries to reclaim synchronously when there are too many entries
56 * in cache
57 */
58#define SYNC_SHRINK_BATCH 64
59
60/*
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?
67 *
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.
71 */
72int mb_cache_entry_create(struct mb_cache *cache, gfp_t mask, u32 key,
73 sector_t block, bool reusable)
74{
75 struct mb_cache_entry *entry, *dup;
76 struct hlist_bl_node *dup_node;
77 struct hlist_bl_head *head;
78
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);
85
86 entry = kmem_cache_alloc(mb_entry_cache, mask);
87 if (!entry)
88 return -ENOMEM;
89
90 INIT_LIST_HEAD(&entry->e_list);
91 /* One ref for hash, one ref returned */
92 atomic_set(&entry->e_refcnt, 1);
93 entry->e_key = key;
94 entry->e_block = block;
95 entry->e_reusable = reusable;
96 entry->e_referenced = 0;
97 head = mb_cache_entry_head(cache, key);
98 hlist_bl_lock(head);
99 hlist_bl_for_each_entry(dup, dup_node, head, e_hash_list) {
100 if (dup->e_key == key && dup->e_block == block) {
101 hlist_bl_unlock(head);
102 kmem_cache_free(mb_entry_cache, entry);
103 return -EBUSY;
104 }
105 }
106 hlist_bl_add_head(&entry->e_hash_list, head);
107 hlist_bl_unlock(head);
108
109 spin_lock(&cache->c_list_lock);
110 list_add_tail(&entry->e_list, &cache->c_list);
111 /* Grab ref for LRU list */
112 atomic_inc(&entry->e_refcnt);
113 cache->c_entry_count++;
114 spin_unlock(&cache->c_list_lock);
115
116 return 0;
117}
118EXPORT_SYMBOL(mb_cache_entry_create);
119
120void __mb_cache_entry_free(struct mb_cache_entry *entry)
121{
122 kmem_cache_free(mb_entry_cache, entry);
123}
124EXPORT_SYMBOL(__mb_cache_entry_free);
125
126static struct mb_cache_entry *__entry_find(struct mb_cache *cache,
127 struct mb_cache_entry *entry,
128 u32 key)
129{
130 struct mb_cache_entry *old_entry = entry;
131 struct hlist_bl_node *node;
132 struct hlist_bl_head *head;
133
134 head = mb_cache_entry_head(cache, key);
135 hlist_bl_lock(head);
136 if (entry && !hlist_bl_unhashed(&entry->e_hash_list))
137 node = entry->e_hash_list.next;
138 else
139 node = hlist_bl_first(head);
140 while (node) {
141 entry = hlist_bl_entry(node, struct mb_cache_entry,
142 e_hash_list);
143 if (entry->e_key == key && entry->e_reusable) {
144 atomic_inc(&entry->e_refcnt);
145 goto out;
146 }
147 node = node->next;
148 }
149 entry = NULL;
150out:
151 hlist_bl_unlock(head);
152 if (old_entry)
153 mb_cache_entry_put(cache, old_entry);
154
155 return entry;
156}
157
158/*
159 * mb_cache_entry_find_first - find the first entry in cache with given key
160 * @cache: cache where we should search
161 * @key: key to look for
162 *
163 * Search in @cache for entry with key @key. Grabs reference to the first
164 * entry found and returns the entry.
165 */
166struct mb_cache_entry *mb_cache_entry_find_first(struct mb_cache *cache,
167 u32 key)
168{
169 return __entry_find(cache, NULL, key);
170}
171EXPORT_SYMBOL(mb_cache_entry_find_first);
172
173/*
174 * mb_cache_entry_find_next - find next entry in cache with the same
175 * @cache: cache where we should search
176 * @entry: entry to start search from
177 *
178 * Finds next entry in the hash chain which has the same key as @entry.
179 * If @entry is unhashed (which can happen when deletion of entry races
180 * with the search), finds the first entry in the hash chain. The function
181 * drops reference to @entry and returns with a reference to the found entry.
182 */
183struct mb_cache_entry *mb_cache_entry_find_next(struct mb_cache *cache,
184 struct mb_cache_entry *entry)
185{
186 return __entry_find(cache, entry, entry->e_key);
187}
188EXPORT_SYMBOL(mb_cache_entry_find_next);
189
190/*
191 * mb_cache_entry_get - get a cache entry by block number (and key)
192 * @cache - cache we work with
193 * @key - key of block number @block
194 * @block - block number
195 */
196struct mb_cache_entry *mb_cache_entry_get(struct mb_cache *cache, u32 key,
197 sector_t block)
198{
199 struct hlist_bl_node *node;
200 struct hlist_bl_head *head;
201 struct mb_cache_entry *entry;
202
203 head = mb_cache_entry_head(cache, key);
204 hlist_bl_lock(head);
205 hlist_bl_for_each_entry(entry, node, head, e_hash_list) {
206 if (entry->e_key == key && entry->e_block == block) {
207 atomic_inc(&entry->e_refcnt);
208 goto out;
209 }
210 }
211 entry = NULL;
212out:
213 hlist_bl_unlock(head);
214 return entry;
215}
216EXPORT_SYMBOL(mb_cache_entry_get);
217
218/* mb_cache_entry_delete_block - remove information about block from cache
219 * @cache - cache we work with
220 * @key - key of block @block
221 * @block - block number
222 *
223 * Remove entry from cache @cache with key @key with data stored in @block.
224 */
225void mb_cache_entry_delete_block(struct mb_cache *cache, u32 key,
226 sector_t block)
227{
228 struct hlist_bl_node *node;
229 struct hlist_bl_head *head;
230 struct mb_cache_entry *entry;
231
232 head = mb_cache_entry_head(cache, key);
233 hlist_bl_lock(head);
234 hlist_bl_for_each_entry(entry, node, head, e_hash_list) {
235 if (entry->e_key == key && entry->e_block == block) {
236 /* We keep hash list reference to keep entry alive */
237 hlist_bl_del_init(&entry->e_hash_list);
238 hlist_bl_unlock(head);
239 spin_lock(&cache->c_list_lock);
240 if (!list_empty(&entry->e_list)) {
241 list_del_init(&entry->e_list);
242 cache->c_entry_count--;
243 atomic_dec(&entry->e_refcnt);
244 }
245 spin_unlock(&cache->c_list_lock);
246 mb_cache_entry_put(cache, entry);
247 return;
248 }
249 }
250 hlist_bl_unlock(head);
251}
252EXPORT_SYMBOL(mb_cache_entry_delete_block);
253
254/* mb_cache_entry_touch - cache entry got used
255 * @cache - cache the entry belongs to
256 * @entry - entry that got used
257 *
258 * Marks entry as used to give hit higher chances of surviving in cache.
259 */
260void mb_cache_entry_touch(struct mb_cache *cache,
261 struct mb_cache_entry *entry)
262{
263 entry->e_referenced = 1;
264}
265EXPORT_SYMBOL(mb_cache_entry_touch);
266
267static unsigned long mb_cache_count(struct shrinker *shrink,
268 struct shrink_control *sc)
269{
270 struct mb_cache *cache = container_of(shrink, struct mb_cache,
271 c_shrink);
272
273 return cache->c_entry_count;
274}
275
276/* Shrink number of entries in cache */
277static unsigned long mb_cache_shrink(struct mb_cache *cache,
278 unsigned int nr_to_scan)
279{
280 struct mb_cache_entry *entry;
281 struct hlist_bl_head *head;
282 unsigned int shrunk = 0;
283
284 spin_lock(&cache->c_list_lock);
285 while (nr_to_scan-- && !list_empty(&cache->c_list)) {
286 entry = list_first_entry(&cache->c_list,
287 struct mb_cache_entry, e_list);
288 if (entry->e_referenced) {
289 entry->e_referenced = 0;
290 list_move_tail(&cache->c_list, &entry->e_list);
291 continue;
292 }
293 list_del_init(&entry->e_list);
294 cache->c_entry_count--;
295 /*
296 * We keep LRU list reference so that entry doesn't go away
297 * from under us.
298 */
299 spin_unlock(&cache->c_list_lock);
300 head = mb_cache_entry_head(cache, entry->e_key);
301 hlist_bl_lock(head);
302 if (!hlist_bl_unhashed(&entry->e_hash_list)) {
303 hlist_bl_del_init(&entry->e_hash_list);
304 atomic_dec(&entry->e_refcnt);
305 }
306 hlist_bl_unlock(head);
307 if (mb_cache_entry_put(cache, entry))
308 shrunk++;
309 cond_resched();
310 spin_lock(&cache->c_list_lock);
311 }
312 spin_unlock(&cache->c_list_lock);
313
314 return shrunk;
315}
316
317static unsigned long mb_cache_scan(struct shrinker *shrink,
318 struct shrink_control *sc)
319{
320 int nr_to_scan = sc->nr_to_scan;
321 struct mb_cache *cache = container_of(shrink, struct mb_cache,
322 c_shrink);
323 return mb_cache_shrink(cache, nr_to_scan);
324}
325
326/* We shrink 1/X of the cache when we have too many entries in it */
327#define SHRINK_DIVISOR 16
328
329static void mb_cache_shrink_worker(struct work_struct *work)
330{
331 struct mb_cache *cache = container_of(work, struct mb_cache,
332 c_shrink_work);
333 mb_cache_shrink(cache, cache->c_max_entries / SHRINK_DIVISOR);
334}
335
336/*
337 * mb_cache_create - create cache
338 * @bucket_bits: log2 of the hash table size
339 *
340 * Create cache for keys with 2^bucket_bits hash entries.
341 */
342struct mb_cache *mb_cache_create(int bucket_bits)
343{
344 struct mb_cache *cache;
345 int bucket_count = 1 << bucket_bits;
346 int i;
347
348 if (!try_module_get(THIS_MODULE))
349 return NULL;
350
351 cache = kzalloc(sizeof(struct mb_cache), GFP_KERNEL);
352 if (!cache)
353 goto err_out;
354 cache->c_bucket_bits = bucket_bits;
355 cache->c_max_entries = bucket_count << 4;
356 INIT_LIST_HEAD(&cache->c_list);
357 spin_lock_init(&cache->c_list_lock);
358 cache->c_hash = kmalloc(bucket_count * sizeof(struct hlist_bl_head),
359 GFP_KERNEL);
360 if (!cache->c_hash) {
361 kfree(cache);
362 goto err_out;
363 }
364 for (i = 0; i < bucket_count; i++)
365 INIT_HLIST_BL_HEAD(&cache->c_hash[i]);
366
367 cache->c_shrink.count_objects = mb_cache_count;
368 cache->c_shrink.scan_objects = mb_cache_scan;
369 cache->c_shrink.seeks = DEFAULT_SEEKS;
370 if (register_shrinker(&cache->c_shrink)) {
371 kfree(cache->c_hash);
372 kfree(cache);
373 goto err_out;
374 }
375
376 INIT_WORK(&cache->c_shrink_work, mb_cache_shrink_worker);
377
378 return cache;
379
380err_out:
381 module_put(THIS_MODULE);
382 return NULL;
383}
384EXPORT_SYMBOL(mb_cache_create);
385
386/*
387 * mb_cache_destroy - destroy cache
388 * @cache: the cache to destroy
389 *
390 * Free all entries in cache and cache itself. Caller must make sure nobody
391 * (except shrinker) can reach @cache when calling this.
392 */
393void mb_cache_destroy(struct mb_cache *cache)
394{
395 struct mb_cache_entry *entry, *next;
396
397 unregister_shrinker(&cache->c_shrink);
398
399 /*
400 * We don't bother with any locking. Cache must not be used at this
401 * point.
402 */
403 list_for_each_entry_safe(entry, next, &cache->c_list, e_list) {
404 if (!hlist_bl_unhashed(&entry->e_hash_list)) {
405 hlist_bl_del_init(&entry->e_hash_list);
406 atomic_dec(&entry->e_refcnt);
407 } else
408 WARN_ON(1);
409 list_del(&entry->e_list);
410 WARN_ON(atomic_read(&entry->e_refcnt) != 1);
411 mb_cache_entry_put(cache, entry);
412 }
413 kfree(cache->c_hash);
414 kfree(cache);
415 module_put(THIS_MODULE);
416}
417EXPORT_SYMBOL(mb_cache_destroy);
418
419static int __init mbcache_init(void)
420{
421 mb_entry_cache = kmem_cache_create("mbcache",
422 sizeof(struct mb_cache_entry), 0,
423 SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL);
424 BUG_ON(!mb_entry_cache);
425 return 0;
426}
427
428static void __exit mbcache_exit(void)
429{
430 kmem_cache_destroy(mb_entry_cache);
431}
432
433module_init(mbcache_init)
434module_exit(mbcache_exit)
435
436MODULE_AUTHOR("Jan Kara <jack@suse.cz>");
437MODULE_DESCRIPTION("Meta block cache (for extended attributes)");
438MODULE_LICENSE("GPL");
439
generated by cgit at 2024-05-18 11:15:29 (GMT)