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CommitLineData
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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>
c2f3140f 7#include <linux/workqueue.h>
7a2508e1 8#include <linux/mbcache.h>
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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
7a2508e1 13 * mb_cache_entry_delete_block()).
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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
7a2508e1 26struct mb_cache {
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27 /* Hash table of entries */
28 struct hlist_bl_head *c_hash;
29 /* log2 of hash table size */
30 int c_bucket_bits;
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31 /* Maximum entries in cache to avoid degrading hash too much */
32 int c_max_entries;
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33 /* Protects c_list, c_entry_count */
34 spinlock_t c_list_lock;
35 struct list_head c_list;
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36 /* Number of entries in cache */
37 unsigned long c_entry_count;
38 struct shrinker c_shrink;
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39 /* Work for shrinking when the cache has too many entries */
40 struct work_struct c_shrink_work;
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41};
42
7a2508e1 43static struct kmem_cache *mb_entry_cache;
f9a61eb4 44
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45static unsigned long mb_cache_shrink(struct mb_cache *cache,
46 unsigned int nr_to_scan);
c2f3140f 47
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48static inline struct hlist_bl_head *mb_cache_entry_head(struct mb_cache *cache,
49 u32 key)
f0c8b462 50{
dc8d5e56 51 return &cache->c_hash[hash_32(key, cache->c_bucket_bits)];
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52}
53
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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
f9a61eb4 60/*
7a2508e1 61 * mb_cache_entry_create - create entry in cache
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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
6048c64b 66 * @reusable - is the block reusable by other inodes?
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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 */
7a2508e1 72int mb_cache_entry_create(struct mb_cache *cache, gfp_t mask, u32 key,
6048c64b 73 sector_t block, bool reusable)
f9a61eb4 74{
7a2508e1 75 struct mb_cache_entry *entry, *dup;
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76 struct hlist_bl_node *dup_node;
77 struct hlist_bl_head *head;
78
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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)
7a2508e1 84 mb_cache_shrink(cache, SYNC_SHRINK_BATCH);
c2f3140f 85
7a2508e1 86 entry = kmem_cache_alloc(mb_entry_cache, mask);
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87 if (!entry)
88 return -ENOMEM;
89
f0c8b462 90 INIT_LIST_HEAD(&entry->e_list);
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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;
6048c64b 95 entry->e_reusable = reusable;
dc8d5e56 96 head = mb_cache_entry_head(cache, key);
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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);
7a2508e1 101 kmem_cache_free(mb_entry_cache, entry);
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102 return -EBUSY;
103 }
104 }
105 hlist_bl_add_head(&entry->e_hash_list, head);
106 hlist_bl_unlock(head);
107
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108 spin_lock(&cache->c_list_lock);
109 list_add_tail(&entry->e_list, &cache->c_list);
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110 /* Grab ref for LRU list */
111 atomic_inc(&entry->e_refcnt);
112 cache->c_entry_count++;
f0c8b462 113 spin_unlock(&cache->c_list_lock);
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114
115 return 0;
116}
7a2508e1 117EXPORT_SYMBOL(mb_cache_entry_create);
f9a61eb4 118
7a2508e1 119void __mb_cache_entry_free(struct mb_cache_entry *entry)
f9a61eb4 120{
7a2508e1 121 kmem_cache_free(mb_entry_cache, entry);
f9a61eb4 122}
7a2508e1 123EXPORT_SYMBOL(__mb_cache_entry_free);
f9a61eb4 124
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125static struct mb_cache_entry *__entry_find(struct mb_cache *cache,
126 struct mb_cache_entry *entry,
127 u32 key)
f9a61eb4 128{
7a2508e1 129 struct mb_cache_entry *old_entry = entry;
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130 struct hlist_bl_node *node;
131 struct hlist_bl_head *head;
132
dc8d5e56 133 head = mb_cache_entry_head(cache, key);
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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) {
7a2508e1 140 entry = hlist_bl_entry(node, struct mb_cache_entry,
f9a61eb4 141 e_hash_list);
6048c64b 142 if (entry->e_key == key && entry->e_reusable) {
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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)
7a2508e1 152 mb_cache_entry_put(cache, old_entry);
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153
154 return entry;
155}
156
157/*
7a2508e1 158 * mb_cache_entry_find_first - find the first entry in cache with given key
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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 */
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165struct mb_cache_entry *mb_cache_entry_find_first(struct mb_cache *cache,
166 u32 key)
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167{
168 return __entry_find(cache, NULL, key);
169}
7a2508e1 170EXPORT_SYMBOL(mb_cache_entry_find_first);
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171
172/*
7a2508e1 173 * mb_cache_entry_find_next - find next entry in cache with the same
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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 */
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182struct mb_cache_entry *mb_cache_entry_find_next(struct mb_cache *cache,
183 struct mb_cache_entry *entry)
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184{
185 return __entry_find(cache, entry, entry->e_key);
186}
7a2508e1 187EXPORT_SYMBOL(mb_cache_entry_find_next);
f9a61eb4 188
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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
7a2508e1 217/* mb_cache_entry_delete_block - remove information about block from cache
f9a61eb4 218 * @cache - cache we work with
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219 * @key - key of block @block
220 * @block - block number
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221 *
222 * Remove entry from cache @cache with key @key with data stored in @block.
223 */
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224void mb_cache_entry_delete_block(struct mb_cache *cache, u32 key,
225 sector_t block)
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226{
227 struct hlist_bl_node *node;
228 struct hlist_bl_head *head;
7a2508e1 229 struct mb_cache_entry *entry;
f9a61eb4 230
dc8d5e56 231 head = mb_cache_entry_head(cache, key);
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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);
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238 spin_lock(&cache->c_list_lock);
239 if (!list_empty(&entry->e_list)) {
240 list_del_init(&entry->e_list);
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241 cache->c_entry_count--;
242 atomic_dec(&entry->e_refcnt);
243 }
f0c8b462 244 spin_unlock(&cache->c_list_lock);
7a2508e1 245 mb_cache_entry_put(cache, entry);
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246 return;
247 }
248 }
249 hlist_bl_unlock(head);
250}
7a2508e1 251EXPORT_SYMBOL(mb_cache_entry_delete_block);
f9a61eb4 252
7a2508e1 253/* mb_cache_entry_touch - cache entry got used
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254 * @cache - cache the entry belongs to
255 * @entry - entry that got used
256 *
f0c8b462 257 * Marks entry as used to give hit higher chances of surviving in cache.
f9a61eb4 258 */
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259void mb_cache_entry_touch(struct mb_cache *cache,
260 struct mb_cache_entry *entry)
f9a61eb4 261{
dc8d5e56 262 entry->e_referenced = 1;
f9a61eb4 263}
7a2508e1 264EXPORT_SYMBOL(mb_cache_entry_touch);
f9a61eb4 265
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266static unsigned long mb_cache_count(struct shrinker *shrink,
267 struct shrink_control *sc)
f9a61eb4 268{
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269 struct mb_cache *cache = container_of(shrink, struct mb_cache,
270 c_shrink);
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271
272 return cache->c_entry_count;
273}
274
275/* Shrink number of entries in cache */
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276static unsigned long mb_cache_shrink(struct mb_cache *cache,
277 unsigned int nr_to_scan)
f9a61eb4 278{
7a2508e1 279 struct mb_cache_entry *entry;
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280 struct hlist_bl_head *head;
281 unsigned int shrunk = 0;
282
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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,
7a2508e1 286 struct mb_cache_entry, e_list);
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287 if (entry->e_referenced) {
288 entry->e_referenced = 0;
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289 list_move_tail(&cache->c_list, &entry->e_list);
290 continue;
291 }
292 list_del_init(&entry->e_list);
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293 cache->c_entry_count--;
294 /*
295 * We keep LRU list reference so that entry doesn't go away
296 * from under us.
297 */
f0c8b462 298 spin_unlock(&cache->c_list_lock);
dc8d5e56 299 head = mb_cache_entry_head(cache, entry->e_key);
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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);
7a2508e1 306 if (mb_cache_entry_put(cache, entry))
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307 shrunk++;
308 cond_resched();
f0c8b462 309 spin_lock(&cache->c_list_lock);
f9a61eb4 310 }
f0c8b462 311 spin_unlock(&cache->c_list_lock);
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312
313 return shrunk;
314}
315
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316static unsigned long mb_cache_scan(struct shrinker *shrink,
317 struct shrink_control *sc)
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318{
319 int nr_to_scan = sc->nr_to_scan;
7a2508e1 320 struct mb_cache *cache = container_of(shrink, struct mb_cache,
c2f3140f 321 c_shrink);
7a2508e1 322 return mb_cache_shrink(cache, nr_to_scan);
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323}
324
325/* We shrink 1/X of the cache when we have too many entries in it */
326#define SHRINK_DIVISOR 16
327
7a2508e1 328static void mb_cache_shrink_worker(struct work_struct *work)
c2f3140f 329{
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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);
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333}
334
f9a61eb4 335/*
7a2508e1 336 * mb_cache_create - create cache
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337 * @bucket_bits: log2 of the hash table size
338 *
339 * Create cache for keys with 2^bucket_bits hash entries.
340 */
7a2508e1 341struct mb_cache *mb_cache_create(int bucket_bits)
f9a61eb4 342{
7a2508e1 343 struct mb_cache *cache;
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344 int bucket_count = 1 << bucket_bits;
345 int i;
346
347 if (!try_module_get(THIS_MODULE))
348 return NULL;
349
7a2508e1 350 cache = kzalloc(sizeof(struct mb_cache), GFP_KERNEL);
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351 if (!cache)
352 goto err_out;
353 cache->c_bucket_bits = bucket_bits;
c2f3140f 354 cache->c_max_entries = bucket_count << 4;
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355 INIT_LIST_HEAD(&cache->c_list);
356 spin_lock_init(&cache->c_list_lock);
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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
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366 cache->c_shrink.count_objects = mb_cache_count;
367 cache->c_shrink.scan_objects = mb_cache_scan;
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368 cache->c_shrink.seeks = DEFAULT_SEEKS;
369 register_shrinker(&cache->c_shrink);
370
7a2508e1 371 INIT_WORK(&cache->c_shrink_work, mb_cache_shrink_worker);
c2f3140f 372
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373 return cache;
374
375err_out:
376 module_put(THIS_MODULE);
377 return NULL;
378}
7a2508e1 379EXPORT_SYMBOL(mb_cache_create);
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380
381/*
7a2508e1 382 * mb_cache_destroy - destroy cache
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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 */
7a2508e1 388void mb_cache_destroy(struct mb_cache *cache)
f9a61eb4 389{
7a2508e1 390 struct mb_cache_entry *entry, *next;
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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 */
f0c8b462 398 list_for_each_entry_safe(entry, next, &cache->c_list, e_list) {
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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);
f0c8b462 404 list_del(&entry->e_list);
f9a61eb4 405 WARN_ON(atomic_read(&entry->e_refcnt) != 1);
7a2508e1 406 mb_cache_entry_put(cache, entry);
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407 }
408 kfree(cache->c_hash);
409 kfree(cache);
410 module_put(THIS_MODULE);
411}
7a2508e1 412EXPORT_SYMBOL(mb_cache_destroy);
f9a61eb4 413
7a2508e1 414static int __init mbcache_init(void)
f9a61eb4 415{
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416 mb_entry_cache = kmem_cache_create("mbcache",
417 sizeof(struct mb_cache_entry), 0,
f9a61eb4 418 SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL);
7a2508e1 419 BUG_ON(!mb_entry_cache);
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420 return 0;
421}
422
7a2508e1 423static void __exit mbcache_exit(void)
f9a61eb4 424{
7a2508e1 425 kmem_cache_destroy(mb_entry_cache);
f9a61eb4
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426}
427
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428module_init(mbcache_init)
429module_exit(mbcache_exit)
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430
431MODULE_AUTHOR("Jan Kara <jack@suse.cz>");
432MODULE_DESCRIPTION("Meta block cache (for extended attributes)");
433MODULE_LICENSE("GPL");