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f9a61eb4 JK |
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 | */ | |
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 | ||
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 | ||
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 | */ | |
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 | */ | |
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 | */ | |
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 | */ | |
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 | ||
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 */ | |
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 | */ | |
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 | */ | |
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 | ||
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 | ||
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"); |