projects/linux·blob v4.7 · refs

433 lines · 11.9 KiB

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 head = mb_cache_entry_head(cache, key);
97 hlist_bl_lock(head);
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);
102 return -EBUSY;
103 }
104 }
105 hlist_bl_add_head(&entry->e_hash_list, head);
106 hlist_bl_unlock(head);
107
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);
114
115 return 0;
116}
117EXPORT_SYMBOL(mb_cache_entry_create);
118
119void __mb_cache_entry_free(struct mb_cache_entry *entry)
120{
121 kmem_cache_free(mb_entry_cache, entry);
122}
123EXPORT_SYMBOL(__mb_cache_entry_free);
124
125static struct mb_cache_entry *__entry_find(struct mb_cache *cache,
126 struct mb_cache_entry *entry,
127 u32 key)
128{
129 struct mb_cache_entry *old_entry = entry;
130 struct hlist_bl_node *node;
131 struct hlist_bl_head *head;
132
133 head = mb_cache_entry_head(cache, key);
134 hlist_bl_lock(head);
135 if (entry && !hlist_bl_unhashed(&entry->e_hash_list))
136 node = entry->e_hash_list.next;
137 else
138 node = hlist_bl_first(head);
139 while (node) {
140 entry = hlist_bl_entry(node, struct mb_cache_entry,
141 e_hash_list);
142 if (entry->e_key == key && entry->e_reusable) {
143 atomic_inc(&entry->e_refcnt);
144 goto out;
145 }
146 node = node->next;
147 }
148 entry = NULL;
149out:
150 hlist_bl_unlock(head);
151 if (old_entry)
152 mb_cache_entry_put(cache, old_entry);
153
154 return entry;
155}
156
157/*
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
161 *
162 * Search in @cache for entry with key @key. Grabs reference to the first
163 * entry found and returns the entry.
164 */
165struct mb_cache_entry *mb_cache_entry_find_first(struct mb_cache *cache,
166 u32 key)
167{
168 return __entry_find(cache, NULL, key);
169}
170EXPORT_SYMBOL(mb_cache_entry_find_first);
171
172/*
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
176 *
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.
181 */
182struct mb_cache_entry *mb_cache_entry_find_next(struct mb_cache *cache,
183 struct mb_cache_entry *entry)
184{
185 return __entry_find(cache, entry, entry->e_key);
186}
187EXPORT_SYMBOL(mb_cache_entry_find_next);
188
189/*
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
194 */
195struct mb_cache_entry *mb_cache_entry_get(struct mb_cache *cache, u32 key,
196 sector_t block)
197{
198 struct hlist_bl_node *node;
199 struct hlist_bl_head *head;
200 struct mb_cache_entry *entry;
201
202 head = mb_cache_entry_head(cache, key);
203 hlist_bl_lock(head);
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);
207 goto out;
208 }
209 }
210 entry = NULL;
211out:
212 hlist_bl_unlock(head);
213 return entry;
214}
215EXPORT_SYMBOL(mb_cache_entry_get);
216
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
221 *
222 * Remove entry from cache @cache with key @key with data stored in @block.
223 */
224void mb_cache_entry_delete_block(struct mb_cache *cache, u32 key,
225 sector_t block)
226{
227 struct hlist_bl_node *node;
228 struct hlist_bl_head *head;
229 struct mb_cache_entry *entry;
230
231 head = mb_cache_entry_head(cache, key);
232 hlist_bl_lock(head);
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);
243 }
244 spin_unlock(&cache->c_list_lock);
245 mb_cache_entry_put(cache, entry);
246 return;
247 }
248 }
249 hlist_bl_unlock(head);
250}
251EXPORT_SYMBOL(mb_cache_entry_delete_block);
252
253/* mb_cache_entry_touch - cache entry got used
254 * @cache - cache the entry belongs to
255 * @entry - entry that got used
256 *
257 * Marks entry as used to give hit higher chances of surviving in cache.
258 */
259void mb_cache_entry_touch(struct mb_cache *cache,
260 struct mb_cache_entry *entry)
261{
262 entry->e_referenced = 1;
263}
264EXPORT_SYMBOL(mb_cache_entry_touch);
265
266static unsigned long mb_cache_count(struct shrinker *shrink,
267 struct shrink_control *sc)
268{
269 struct mb_cache *cache = container_of(shrink, struct mb_cache,
270 c_shrink);
271
272 return cache->c_entry_count;
273}
274
275/* Shrink number of entries in cache */
276static unsigned long mb_cache_shrink(struct mb_cache *cache,
277 unsigned int nr_to_scan)
278{
279 struct mb_cache_entry *entry;
280 struct hlist_bl_head *head;
281 unsigned int shrunk = 0;
282
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);
290 continue;
291 }
292 list_del_init(&entry->e_list);
293 cache->c_entry_count--;
294 /*
295 * We keep LRU list reference so that entry doesn't go away
296 * from under us.
297 */
298 spin_unlock(&cache->c_list_lock);
299 head = mb_cache_entry_head(cache, entry->e_key);
300 hlist_bl_lock(head);
301 if (!hlist_bl_unhashed(&entry->e_hash_list)) {
302 hlist_bl_del_init(&entry->e_hash_list);
303 atomic_dec(&entry->e_refcnt);
304 }
305 hlist_bl_unlock(head);
306 if (mb_cache_entry_put(cache, entry))
307 shrunk++;
308 cond_resched();
309 spin_lock(&cache->c_list_lock);
310 }
311 spin_unlock(&cache->c_list_lock);
312
313 return shrunk;
314}
315
316static unsigned long mb_cache_scan(struct shrinker *shrink,
317 struct shrink_control *sc)
318{
319 int nr_to_scan = sc->nr_to_scan;
320 struct mb_cache *cache = container_of(shrink, struct mb_cache,
321 c_shrink);
322 return mb_cache_shrink(cache, nr_to_scan);
323}
324
325/* We shrink 1/X of the cache when we have too many entries in it */
326#define SHRINK_DIVISOR 16
327
328static void mb_cache_shrink_worker(struct work_struct *work)
329{
330 struct mb_cache *cache = container_of(work, struct mb_cache,
331 c_shrink_work);
332 mb_cache_shrink(cache, cache->c_max_entries / SHRINK_DIVISOR);
333}
334
335/*
336 * mb_cache_create - create cache
337 * @bucket_bits: log2 of the hash table size
338 *
339 * Create cache for keys with 2^bucket_bits hash entries.
340 */
341struct mb_cache *mb_cache_create(int bucket_bits)
342{
343 struct mb_cache *cache;
344 int bucket_count = 1 << bucket_bits;
345 int i;
346
347 if (!try_module_get(THIS_MODULE))
348 return NULL;
349
350 cache = kzalloc(sizeof(struct mb_cache), GFP_KERNEL);
351 if (!cache)
352 goto err_out;
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),
358 GFP_KERNEL);
359 if (!cache->c_hash) {
360 kfree(cache);
361 goto err_out;
362 }
363 for (i = 0; i < bucket_count; i++)
364 INIT_HLIST_BL_HEAD(&cache->c_hash[i]);
365
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);
370
371 INIT_WORK(&cache->c_shrink_work, mb_cache_shrink_worker);
372
373 return cache;
374
375err_out:
376 module_put(THIS_MODULE);
377 return NULL;
378}
379EXPORT_SYMBOL(mb_cache_create);
380
381/*
382 * mb_cache_destroy - destroy cache
383 * @cache: the cache to destroy
384 *
385 * Free all entries in cache and cache itself. Caller must make sure nobody
386 * (except shrinker) can reach @cache when calling this.
387 */
388void mb_cache_destroy(struct mb_cache *cache)
389{
390 struct mb_cache_entry *entry, *next;
391
392 unregister_shrinker(&cache->c_shrink);
393
394 /*
395 * We don't bother with any locking. Cache must not be used at this
396 * point.
397 */
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);
402 } else
403 WARN_ON(1);
404 list_del(&entry->e_list);
405 WARN_ON(atomic_read(&entry->e_refcnt) != 1);
406 mb_cache_entry_put(cache, entry);
407 }
408 kfree(cache->c_hash);
409 kfree(cache);
410 module_put(THIS_MODULE);
411}
412EXPORT_SYMBOL(mb_cache_destroy);
413
414static int __init mbcache_init(void)
415{
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);
420 return 0;
421}
422
423static void __exit mbcache_exit(void)
424{
425 kmem_cache_destroy(mb_entry_cache);
426}
427
428module_init(mbcache_init)
429module_exit(mbcache_exit)
430
431MODULE_AUTHOR("Jan Kara <[email protected]>");
432MODULE_DESCRIPTION("Meta block cache (for extended attributes)");
433MODULE_LICENSE("GPL");