1 // SPDX-License-Identifier: GPL-2.0-only 2 #include <linux/spinlock.h> 3 #include <linux/slab.h> 4 #include <linux/list.h> 5 #include <linux/list_bl.h> 6 #include <linux/module.h> 7 #include <linux/sched.h> 8 #include <linux/workqueue.h> 9 #include <linux/mbcache.h> 10 11 /* 12 * Mbcache is a simple key-value store. Keys need not be unique, however 13 * key-value pairs are expected to be unique (we use this fact in 14 * mb_cache_entry_delete()). 15 * 16 * Ext2 and ext4 use this cache for deduplication of extended attribute blocks. 17 * Ext4 also uses it for deduplication of xattr values stored in inodes. 18 * They use hash of data as a key and provide a value that may represent a 19 * block or inode number. That's why keys need not be unique (hash of different 20 * data may be the same). However user provided value always uniquely 21 * identifies a cache entry. 22 * 23 * We provide functions for creation and removal of entries, search by key, 24 * and a special "delete entry with given key-value pair" operation. Fixed 25 * size hash table is used for fast key lookups. 26 */ 27 28 struct mb_cache { 29 /* Hash table of entries */ 30 struct hlist_bl_head *c_hash; 31 /* log2 of hash table size */ 32 int c_bucket_bits; 33 /* Maximum entries in cache to avoid degrading hash too much */ 34 unsigned long c_max_entries; 35 /* Protects c_list, c_entry_count */ 36 spinlock_t c_list_lock; 37 struct list_head c_list; 38 /* Number of entries in cache */ 39 unsigned long c_entry_count; 40 struct shrinker c_shrink; 41 /* Work for shrinking when the cache has too many entries */ 42 struct work_struct c_shrink_work; 43 }; 44 45 static struct kmem_cache *mb_entry_cache; 46 47 static unsigned long mb_cache_shrink(struct mb_cache *cache, 48 unsigned long nr_to_scan); 49 50 static inline struct hlist_bl_head *mb_cache_entry_head(struct mb_cache *cache, 51 u32 key) 52 { 53 return &cache->c_hash[hash_32(key, cache->c_bucket_bits)]; 54 } 55 56 /* 57 * Number of entries to reclaim synchronously when there are too many entries 58 * in cache 59 */ 60 #define SYNC_SHRINK_BATCH 64 61 62 /* 63 * mb_cache_entry_create - create entry in cache 64 * @cache - cache where the entry should be created 65 * @mask - gfp mask with which the entry should be allocated 66 * @key - key of the entry 67 * @value - value of the entry 68 * @reusable - is the entry reusable by others? 69 * 70 * Creates entry in @cache with key @key and value @value. The function returns 71 * -EBUSY if entry with the same key and value already exists in cache. 72 * Otherwise 0 is returned. 73 */ 74 int mb_cache_entry_create(struct mb_cache *cache, gfp_t mask, u32 key, 75 u64 value, bool reusable) 76 { 77 struct mb_cache_entry *entry, *dup; 78 struct hlist_bl_node *dup_node; 79 struct hlist_bl_head *head; 80 81 /* Schedule background reclaim if there are too many entries */ 82 if (cache->c_entry_count >= cache->c_max_entries) 83 schedule_work(&cache->c_shrink_work); 84 /* Do some sync reclaim if background reclaim cannot keep up */ 85 if (cache->c_entry_count >= 2*cache->c_max_entries) 86 mb_cache_shrink(cache, SYNC_SHRINK_BATCH); 87 88 entry = kmem_cache_alloc(mb_entry_cache, mask); 89 if (!entry) 90 return -ENOMEM; 91 92 INIT_LIST_HEAD(&entry->e_list); 93 /* One ref for hash, one ref returned */ 94 atomic_set(&entry->e_refcnt, 1); 95 entry->e_key = key; 96 entry->e_value = value; 97 entry->e_reusable = reusable; 98 entry->e_referenced = 0; 99 head = mb_cache_entry_head(cache, key); 100 hlist_bl_lock(head); 101 hlist_bl_for_each_entry(dup, dup_node, head, e_hash_list) { 102 if (dup->e_key == key && dup->e_value == value) { 103 hlist_bl_unlock(head); 104 kmem_cache_free(mb_entry_cache, entry); 105 return -EBUSY; 106 } 107 } 108 hlist_bl_add_head(&entry->e_hash_list, head); 109 hlist_bl_unlock(head); 110 111 spin_lock(&cache->c_list_lock); 112 list_add_tail(&entry->e_list, &cache->c_list); 113 /* Grab ref for LRU list */ 114 atomic_inc(&entry->e_refcnt); 115 cache->c_entry_count++; 116 spin_unlock(&cache->c_list_lock); 117 118 return 0; 119 } 120 EXPORT_SYMBOL(mb_cache_entry_create); 121 122 void __mb_cache_entry_free(struct mb_cache_entry *entry) 123 { 124 kmem_cache_free(mb_entry_cache, entry); 125 } 126 EXPORT_SYMBOL(__mb_cache_entry_free); 127 128 static struct mb_cache_entry *__entry_find(struct mb_cache *cache, 129 struct mb_cache_entry *entry, 130 u32 key) 131 { 132 struct mb_cache_entry *old_entry = entry; 133 struct hlist_bl_node *node; 134 struct hlist_bl_head *head; 135 136 head = mb_cache_entry_head(cache, key); 137 hlist_bl_lock(head); 138 if (entry && !hlist_bl_unhashed(&entry->e_hash_list)) 139 node = entry->e_hash_list.next; 140 else 141 node = hlist_bl_first(head); 142 while (node) { 143 entry = hlist_bl_entry(node, struct mb_cache_entry, 144 e_hash_list); 145 if (entry->e_key == key && entry->e_reusable) { 146 atomic_inc(&entry->e_refcnt); 147 goto out; 148 } 149 node = node->next; 150 } 151 entry = NULL; 152 out: 153 hlist_bl_unlock(head); 154 if (old_entry) 155 mb_cache_entry_put(cache, old_entry); 156 157 return entry; 158 } 159 160 /* 161 * mb_cache_entry_find_first - find the first reusable entry with the given key 162 * @cache: cache where we should search 163 * @key: key to look for 164 * 165 * Search in @cache for a reusable entry with key @key. Grabs reference to the 166 * first reusable entry found and returns the entry. 167 */ 168 struct mb_cache_entry *mb_cache_entry_find_first(struct mb_cache *cache, 169 u32 key) 170 { 171 return __entry_find(cache, NULL, key); 172 } 173 EXPORT_SYMBOL(mb_cache_entry_find_first); 174 175 /* 176 * mb_cache_entry_find_next - find next reusable entry with the same key 177 * @cache: cache where we should search 178 * @entry: entry to start search from 179 * 180 * Finds next reusable entry in the hash chain which has the same key as @entry. 181 * If @entry is unhashed (which can happen when deletion of entry races with the 182 * search), finds the first reusable entry in the hash chain. The function drops 183 * reference to @entry and returns with a reference to the found entry. 184 */ 185 struct mb_cache_entry *mb_cache_entry_find_next(struct mb_cache *cache, 186 struct mb_cache_entry *entry) 187 { 188 return __entry_find(cache, entry, entry->e_key); 189 } 190 EXPORT_SYMBOL(mb_cache_entry_find_next); 191 192 /* 193 * mb_cache_entry_get - get a cache entry by value (and key) 194 * @cache - cache we work with 195 * @key - key 196 * @value - value 197 */ 198 struct mb_cache_entry *mb_cache_entry_get(struct mb_cache *cache, u32 key, 199 u64 value) 200 { 201 struct hlist_bl_node *node; 202 struct hlist_bl_head *head; 203 struct mb_cache_entry *entry; 204 205 head = mb_cache_entry_head(cache, key); 206 hlist_bl_lock(head); 207 hlist_bl_for_each_entry(entry, node, head, e_hash_list) { 208 if (entry->e_key == key && entry->e_value == value) { 209 atomic_inc(&entry->e_refcnt); 210 goto out; 211 } 212 } 213 entry = NULL; 214 out: 215 hlist_bl_unlock(head); 216 return entry; 217 } 218 EXPORT_SYMBOL(mb_cache_entry_get); 219 220 /* mb_cache_entry_delete - remove a cache entry 221 * @cache - cache we work with 222 * @key - key 223 * @value - value 224 * 225 * Remove entry from cache @cache with key @key and value @value. 226 */ 227 void mb_cache_entry_delete(struct mb_cache *cache, u32 key, u64 value) 228 { 229 struct hlist_bl_node *node; 230 struct hlist_bl_head *head; 231 struct mb_cache_entry *entry; 232 233 head = mb_cache_entry_head(cache, key); 234 hlist_bl_lock(head); 235 hlist_bl_for_each_entry(entry, node, head, e_hash_list) { 236 if (entry->e_key == key && entry->e_value == value) { 237 /* We keep hash list reference to keep entry alive */ 238 hlist_bl_del_init(&entry->e_hash_list); 239 hlist_bl_unlock(head); 240 spin_lock(&cache->c_list_lock); 241 if (!list_empty(&entry->e_list)) { 242 list_del_init(&entry->e_list); 243 if (!WARN_ONCE(cache->c_entry_count == 0, 244 "mbcache: attempt to decrement c_entry_count past zero")) 245 cache->c_entry_count--; 246 atomic_dec(&entry->e_refcnt); 247 } 248 spin_unlock(&cache->c_list_lock); 249 mb_cache_entry_put(cache, entry); 250 return; 251 } 252 } 253 hlist_bl_unlock(head); 254 } 255 EXPORT_SYMBOL(mb_cache_entry_delete); 256 257 /* mb_cache_entry_touch - cache entry got used 258 * @cache - cache the entry belongs to 259 * @entry - entry that got used 260 * 261 * Marks entry as used to give hit higher chances of surviving in cache. 262 */ 263 void mb_cache_entry_touch(struct mb_cache *cache, 264 struct mb_cache_entry *entry) 265 { 266 entry->e_referenced = 1; 267 } 268 EXPORT_SYMBOL(mb_cache_entry_touch); 269 270 static unsigned long mb_cache_count(struct shrinker *shrink, 271 struct shrink_control *sc) 272 { 273 struct mb_cache *cache = container_of(shrink, struct mb_cache, 274 c_shrink); 275 276 return cache->c_entry_count; 277 } 278 279 /* Shrink number of entries in cache */ 280 static unsigned long mb_cache_shrink(struct mb_cache *cache, 281 unsigned long nr_to_scan) 282 { 283 struct mb_cache_entry *entry; 284 struct hlist_bl_head *head; 285 unsigned long shrunk = 0; 286 287 spin_lock(&cache->c_list_lock); 288 while (nr_to_scan-- && !list_empty(&cache->c_list)) { 289 entry = list_first_entry(&cache->c_list, 290 struct mb_cache_entry, e_list); 291 if (entry->e_referenced) { 292 entry->e_referenced = 0; 293 list_move_tail(&entry->e_list, &cache->c_list); 294 continue; 295 } 296 list_del_init(&entry->e_list); 297 cache->c_entry_count--; 298 /* 299 * We keep LRU list reference so that entry doesn't go away 300 * from under us. 301 */ 302 spin_unlock(&cache->c_list_lock); 303 head = mb_cache_entry_head(cache, entry->e_key); 304 hlist_bl_lock(head); 305 if (!hlist_bl_unhashed(&entry->e_hash_list)) { 306 hlist_bl_del_init(&entry->e_hash_list); 307 atomic_dec(&entry->e_refcnt); 308 } 309 hlist_bl_unlock(head); 310 if (mb_cache_entry_put(cache, entry)) 311 shrunk++; 312 cond_resched(); 313 spin_lock(&cache->c_list_lock); 314 } 315 spin_unlock(&cache->c_list_lock); 316 317 return shrunk; 318 } 319 320 static unsigned long mb_cache_scan(struct shrinker *shrink, 321 struct shrink_control *sc) 322 { 323 struct mb_cache *cache = container_of(shrink, struct mb_cache, 324 c_shrink); 325 return mb_cache_shrink(cache, sc->nr_to_scan); 326 } 327 328 /* We shrink 1/X of the cache when we have too many entries in it */ 329 #define SHRINK_DIVISOR 16 330 331 static void mb_cache_shrink_worker(struct work_struct *work) 332 { 333 struct mb_cache *cache = container_of(work, struct mb_cache, 334 c_shrink_work); 335 mb_cache_shrink(cache, cache->c_max_entries / SHRINK_DIVISOR); 336 } 337 338 /* 339 * mb_cache_create - create cache 340 * @bucket_bits: log2 of the hash table size 341 * 342 * Create cache for keys with 2^bucket_bits hash entries. 343 */ 344 struct mb_cache *mb_cache_create(int bucket_bits) 345 { 346 struct mb_cache *cache; 347 unsigned long bucket_count = 1UL << bucket_bits; 348 unsigned long i; 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_array(bucket_count, 358 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; 379 380 err_out: 381 return NULL; 382 } 383 EXPORT_SYMBOL(mb_cache_create); 384 385 /* 386 * mb_cache_destroy - destroy cache 387 * @cache: the cache to destroy 388 * 389 * Free all entries in cache and cache itself. Caller must make sure nobody 390 * (except shrinker) can reach @cache when calling this. 391 */ 392 void mb_cache_destroy(struct mb_cache *cache) 393 { 394 struct mb_cache_entry *entry, *next; 395 396 unregister_shrinker(&cache->c_shrink); 397 398 /* 399 * We don't bother with any locking. Cache must not be used at this 400 * point. 401 */ 402 list_for_each_entry_safe(entry, next, &cache->c_list, e_list) { 403 if (!hlist_bl_unhashed(&entry->e_hash_list)) { 404 hlist_bl_del_init(&entry->e_hash_list); 405 atomic_dec(&entry->e_refcnt); 406 } else 407 WARN_ON(1); 408 list_del(&entry->e_list); 409 WARN_ON(atomic_read(&entry->e_refcnt) != 1); 410 mb_cache_entry_put(cache, entry); 411 } 412 kfree(cache->c_hash); 413 kfree(cache); 414 } 415 EXPORT_SYMBOL(mb_cache_destroy); 416 417 static int __init mbcache_init(void) 418 { 419 mb_entry_cache = kmem_cache_create("mbcache", 420 sizeof(struct mb_cache_entry), 0, 421 SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL); 422 if (!mb_entry_cache) 423 return -ENOMEM; 424 return 0; 425 } 426 427 static void __exit mbcache_exit(void) 428 { 429 kmem_cache_destroy(mb_entry_cache); 430 } 431 432 module_init(mbcache_init) 433 module_exit(mbcache_exit) 434 435 MODULE_AUTHOR("Jan Kara <jack@suse.cz>"); 436 MODULE_DESCRIPTION("Meta block cache (for extended attributes)"); 437 MODULE_LICENSE("GPL"); 438