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/mbcache2.h>
8
9 /*
10 * Mbcache is a simple key-value store. Keys need not be unique, however
11 * key-value pairs are expected to be unique (we use this fact in
12 * mb2_cache_entry_delete_block()).
13 *
14 * Ext2 and ext4 use this cache for deduplication of extended attribute blocks.
15 * They use hash of a block contents as a key and block number as a value.
16 * That's why keys need not be unique (different xattr blocks may end up having
17 * the same hash). However block number always uniquely identifies a cache
18 * entry.
19 *
20 * We provide functions for creation and removal of entries, search by key,
21 * and a special "delete entry with given key-value pair" operation. Fixed
22 * size hash table is used for fast key lookups.
23 */
24
25 struct mb2_cache {
26 /* Hash table of entries */
27 struct hlist_bl_head *c_hash;
28 /* log2 of hash table size */
29 int c_bucket_bits;
30 /* Protects c_lru_list, c_entry_count */
31 spinlock_t c_lru_list_lock;
32 struct list_head c_lru_list;
33 /* Number of entries in cache */
34 unsigned long c_entry_count;
35 struct shrinker c_shrink;
36 };
37
38 static struct kmem_cache *mb2_entry_cache;
39
40 /*
41 * mb2_cache_entry_create - create entry in cache
42 * @cache - cache where the entry should be created
43 * @mask - gfp mask with which the entry should be allocated
44 * @key - key of the entry
45 * @block - block that contains data
46 *
47 * Creates entry in @cache with key @key and records that data is stored in
48 * block @block. The function returns -EBUSY if entry with the same key
49 * and for the same block already exists in cache. Otherwise 0 is returned.
50 */
mb2_cache_entry_create(struct mb2_cache * cache,gfp_t mask,u32 key,sector_t block)51 int mb2_cache_entry_create(struct mb2_cache *cache, gfp_t mask, u32 key,
52 sector_t block)
53 {
54 struct mb2_cache_entry *entry, *dup;
55 struct hlist_bl_node *dup_node;
56 struct hlist_bl_head *head;
57
58 entry = kmem_cache_alloc(mb2_entry_cache, mask);
59 if (!entry)
60 return -ENOMEM;
61
62 INIT_LIST_HEAD(&entry->e_lru_list);
63 /* One ref for hash, one ref returned */
64 atomic_set(&entry->e_refcnt, 1);
65 entry->e_key = key;
66 entry->e_block = block;
67 head = &cache->c_hash[hash_32(key, cache->c_bucket_bits)];
68 entry->e_hash_list_head = head;
69 hlist_bl_lock(head);
70 hlist_bl_for_each_entry(dup, dup_node, head, e_hash_list) {
71 if (dup->e_key == key && dup->e_block == block) {
72 hlist_bl_unlock(head);
73 kmem_cache_free(mb2_entry_cache, entry);
74 return -EBUSY;
75 }
76 }
77 hlist_bl_add_head(&entry->e_hash_list, head);
78 hlist_bl_unlock(head);
79
80 spin_lock(&cache->c_lru_list_lock);
81 list_add_tail(&entry->e_lru_list, &cache->c_lru_list);
82 /* Grab ref for LRU list */
83 atomic_inc(&entry->e_refcnt);
84 cache->c_entry_count++;
85 spin_unlock(&cache->c_lru_list_lock);
86
87 return 0;
88 }
89 EXPORT_SYMBOL(mb2_cache_entry_create);
90
__mb2_cache_entry_free(struct mb2_cache_entry * entry)91 void __mb2_cache_entry_free(struct mb2_cache_entry *entry)
92 {
93 kmem_cache_free(mb2_entry_cache, entry);
94 }
95 EXPORT_SYMBOL(__mb2_cache_entry_free);
96
__entry_find(struct mb2_cache * cache,struct mb2_cache_entry * entry,u32 key)97 static struct mb2_cache_entry *__entry_find(struct mb2_cache *cache,
98 struct mb2_cache_entry *entry,
99 u32 key)
100 {
101 struct mb2_cache_entry *old_entry = entry;
102 struct hlist_bl_node *node;
103 struct hlist_bl_head *head;
104
105 if (entry)
106 head = entry->e_hash_list_head;
107 else
108 head = &cache->c_hash[hash_32(key, cache->c_bucket_bits)];
109 hlist_bl_lock(head);
110 if (entry && !hlist_bl_unhashed(&entry->e_hash_list))
111 node = entry->e_hash_list.next;
112 else
113 node = hlist_bl_first(head);
114 while (node) {
115 entry = hlist_bl_entry(node, struct mb2_cache_entry,
116 e_hash_list);
117 if (entry->e_key == key) {
118 atomic_inc(&entry->e_refcnt);
119 goto out;
120 }
121 node = node->next;
122 }
123 entry = NULL;
124 out:
125 hlist_bl_unlock(head);
126 if (old_entry)
127 mb2_cache_entry_put(cache, old_entry);
128
129 return entry;
130 }
131
132 /*
133 * mb2_cache_entry_find_first - find the first entry in cache with given key
134 * @cache: cache where we should search
135 * @key: key to look for
136 *
137 * Search in @cache for entry with key @key. Grabs reference to the first
138 * entry found and returns the entry.
139 */
mb2_cache_entry_find_first(struct mb2_cache * cache,u32 key)140 struct mb2_cache_entry *mb2_cache_entry_find_first(struct mb2_cache *cache,
141 u32 key)
142 {
143 return __entry_find(cache, NULL, key);
144 }
145 EXPORT_SYMBOL(mb2_cache_entry_find_first);
146
147 /*
148 * mb2_cache_entry_find_next - find next entry in cache with the same
149 * @cache: cache where we should search
150 * @entry: entry to start search from
151 *
152 * Finds next entry in the hash chain which has the same key as @entry.
153 * If @entry is unhashed (which can happen when deletion of entry races
154 * with the search), finds the first entry in the hash chain. The function
155 * drops reference to @entry and returns with a reference to the found entry.
156 */
mb2_cache_entry_find_next(struct mb2_cache * cache,struct mb2_cache_entry * entry)157 struct mb2_cache_entry *mb2_cache_entry_find_next(struct mb2_cache *cache,
158 struct mb2_cache_entry *entry)
159 {
160 return __entry_find(cache, entry, entry->e_key);
161 }
162 EXPORT_SYMBOL(mb2_cache_entry_find_next);
163
164 /* mb2_cache_entry_delete_block - remove information about block from cache
165 * @cache - cache we work with
166 * @key - key of the entry to remove
167 * @block - block containing data for @key
168 *
169 * Remove entry from cache @cache with key @key with data stored in @block.
170 */
mb2_cache_entry_delete_block(struct mb2_cache * cache,u32 key,sector_t block)171 void mb2_cache_entry_delete_block(struct mb2_cache *cache, u32 key,
172 sector_t block)
173 {
174 struct hlist_bl_node *node;
175 struct hlist_bl_head *head;
176 struct mb2_cache_entry *entry;
177
178 head = &cache->c_hash[hash_32(key, cache->c_bucket_bits)];
179 hlist_bl_lock(head);
180 hlist_bl_for_each_entry(entry, node, head, e_hash_list) {
181 if (entry->e_key == key && entry->e_block == block) {
182 /* We keep hash list reference to keep entry alive */
183 hlist_bl_del_init(&entry->e_hash_list);
184 hlist_bl_unlock(head);
185 spin_lock(&cache->c_lru_list_lock);
186 if (!list_empty(&entry->e_lru_list)) {
187 list_del_init(&entry->e_lru_list);
188 cache->c_entry_count--;
189 atomic_dec(&entry->e_refcnt);
190 }
191 spin_unlock(&cache->c_lru_list_lock);
192 mb2_cache_entry_put(cache, entry);
193 return;
194 }
195 }
196 hlist_bl_unlock(head);
197 }
198 EXPORT_SYMBOL(mb2_cache_entry_delete_block);
199
200 /* mb2_cache_entry_touch - cache entry got used
201 * @cache - cache the entry belongs to
202 * @entry - entry that got used
203 *
204 * Move entry in lru list to reflect the fact that it was used.
205 */
mb2_cache_entry_touch(struct mb2_cache * cache,struct mb2_cache_entry * entry)206 void mb2_cache_entry_touch(struct mb2_cache *cache,
207 struct mb2_cache_entry *entry)
208 {
209 spin_lock(&cache->c_lru_list_lock);
210 if (!list_empty(&entry->e_lru_list))
211 list_move_tail(&cache->c_lru_list, &entry->e_lru_list);
212 spin_unlock(&cache->c_lru_list_lock);
213 }
214 EXPORT_SYMBOL(mb2_cache_entry_touch);
215
mb2_cache_count(struct shrinker * shrink,struct shrink_control * sc)216 static unsigned long mb2_cache_count(struct shrinker *shrink,
217 struct shrink_control *sc)
218 {
219 struct mb2_cache *cache = container_of(shrink, struct mb2_cache,
220 c_shrink);
221
222 return cache->c_entry_count;
223 }
224
225 /* Shrink number of entries in cache */
mb2_cache_scan(struct shrinker * shrink,struct shrink_control * sc)226 static unsigned long mb2_cache_scan(struct shrinker *shrink,
227 struct shrink_control *sc)
228 {
229 int nr_to_scan = sc->nr_to_scan;
230 struct mb2_cache *cache = container_of(shrink, struct mb2_cache,
231 c_shrink);
232 struct mb2_cache_entry *entry;
233 struct hlist_bl_head *head;
234 unsigned int shrunk = 0;
235
236 spin_lock(&cache->c_lru_list_lock);
237 while (nr_to_scan-- && !list_empty(&cache->c_lru_list)) {
238 entry = list_first_entry(&cache->c_lru_list,
239 struct mb2_cache_entry, e_lru_list);
240 list_del_init(&entry->e_lru_list);
241 cache->c_entry_count--;
242 /*
243 * We keep LRU list reference so that entry doesn't go away
244 * from under us.
245 */
246 spin_unlock(&cache->c_lru_list_lock);
247 head = entry->e_hash_list_head;
248 hlist_bl_lock(head);
249 if (!hlist_bl_unhashed(&entry->e_hash_list)) {
250 hlist_bl_del_init(&entry->e_hash_list);
251 atomic_dec(&entry->e_refcnt);
252 }
253 hlist_bl_unlock(head);
254 if (mb2_cache_entry_put(cache, entry))
255 shrunk++;
256 cond_resched();
257 spin_lock(&cache->c_lru_list_lock);
258 }
259 spin_unlock(&cache->c_lru_list_lock);
260
261 return shrunk;
262 }
263
264 /*
265 * mb2_cache_create - create cache
266 * @bucket_bits: log2 of the hash table size
267 *
268 * Create cache for keys with 2^bucket_bits hash entries.
269 */
mb2_cache_create(int bucket_bits)270 struct mb2_cache *mb2_cache_create(int bucket_bits)
271 {
272 struct mb2_cache *cache;
273 int bucket_count = 1 << bucket_bits;
274 int i;
275
276 if (!try_module_get(THIS_MODULE))
277 return NULL;
278
279 cache = kzalloc(sizeof(struct mb2_cache), GFP_KERNEL);
280 if (!cache)
281 goto err_out;
282 cache->c_bucket_bits = bucket_bits;
283 INIT_LIST_HEAD(&cache->c_lru_list);
284 spin_lock_init(&cache->c_lru_list_lock);
285 cache->c_hash = kmalloc(bucket_count * sizeof(struct hlist_bl_head),
286 GFP_KERNEL);
287 if (!cache->c_hash) {
288 kfree(cache);
289 goto err_out;
290 }
291 for (i = 0; i < bucket_count; i++)
292 INIT_HLIST_BL_HEAD(&cache->c_hash[i]);
293
294 cache->c_shrink.count_objects = mb2_cache_count;
295 cache->c_shrink.scan_objects = mb2_cache_scan;
296 cache->c_shrink.seeks = DEFAULT_SEEKS;
297 register_shrinker(&cache->c_shrink);
298
299 return cache;
300
301 err_out:
302 module_put(THIS_MODULE);
303 return NULL;
304 }
305 EXPORT_SYMBOL(mb2_cache_create);
306
307 /*
308 * mb2_cache_destroy - destroy cache
309 * @cache: the cache to destroy
310 *
311 * Free all entries in cache and cache itself. Caller must make sure nobody
312 * (except shrinker) can reach @cache when calling this.
313 */
mb2_cache_destroy(struct mb2_cache * cache)314 void mb2_cache_destroy(struct mb2_cache *cache)
315 {
316 struct mb2_cache_entry *entry, *next;
317
318 unregister_shrinker(&cache->c_shrink);
319
320 /*
321 * We don't bother with any locking. Cache must not be used at this
322 * point.
323 */
324 list_for_each_entry_safe(entry, next, &cache->c_lru_list, e_lru_list) {
325 if (!hlist_bl_unhashed(&entry->e_hash_list)) {
326 hlist_bl_del_init(&entry->e_hash_list);
327 atomic_dec(&entry->e_refcnt);
328 } else
329 WARN_ON(1);
330 list_del(&entry->e_lru_list);
331 WARN_ON(atomic_read(&entry->e_refcnt) != 1);
332 mb2_cache_entry_put(cache, entry);
333 }
334 kfree(cache->c_hash);
335 kfree(cache);
336 module_put(THIS_MODULE);
337 }
338 EXPORT_SYMBOL(mb2_cache_destroy);
339
mb2cache_init(void)340 static int __init mb2cache_init(void)
341 {
342 mb2_entry_cache = kmem_cache_create("mbcache",
343 sizeof(struct mb2_cache_entry), 0,
344 SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL);
345 BUG_ON(!mb2_entry_cache);
346 return 0;
347 }
348
mb2cache_exit(void)349 static void __exit mb2cache_exit(void)
350 {
351 kmem_cache_destroy(mb2_entry_cache);
352 }
353
354 module_init(mb2cache_init)
355 module_exit(mb2cache_exit)
356
357 MODULE_AUTHOR("Jan Kara <jack@suse.cz>");
358 MODULE_DESCRIPTION("Meta block cache (for extended attributes)");
359 MODULE_LICENSE("GPL");
360