1 /* 2 * linux/fs/mbcache.c 3 * (C) 2001-2002 Andreas Gruenbacher, <a.gruenbacher@computer.org> 4 */ 5 6 /* 7 * Filesystem Meta Information Block Cache (mbcache) 8 * 9 * The mbcache caches blocks of block devices that need to be located 10 * by their device/block number, as well as by other criteria (such 11 * as the block's contents). 12 * 13 * There can only be one cache entry in a cache per device and block number. 14 * Additional indexes need not be unique in this sense. The number of 15 * additional indexes (=other criteria) can be hardwired at compile time 16 * or specified at cache create time. 17 * 18 * Each cache entry is of fixed size. An entry may be `valid' or `invalid' 19 * in the cache. A valid entry is in the main hash tables of the cache, 20 * and may also be in the lru list. An invalid entry is not in any hashes 21 * or lists. 22 * 23 * A valid cache entry is only in the lru list if no handles refer to it. 24 * Invalid cache entries will be freed when the last handle to the cache 25 * entry is released. Entries that cannot be freed immediately are put 26 * back on the lru list. 27 */ 28 29 /* 30 * Lock descriptions and usage: 31 * 32 * Each hash chain of both the block and index hash tables now contains 33 * a built-in lock used to serialize accesses to the hash chain. 34 * 35 * Accesses to global data structures mb_cache_list and mb_cache_lru_list 36 * are serialized via the global spinlock mb_cache_spinlock. 37 * 38 * Each mb_cache_entry contains a spinlock, e_entry_lock, to serialize 39 * accesses to its local data, such as e_used and e_queued. 40 * 41 * Lock ordering: 42 * 43 * Each block hash chain's lock has the highest lock order, followed by an 44 * index hash chain's lock, mb_cache_bg_lock (used to implement mb_cache_entry's 45 * lock), and mb_cach_spinlock, with the lowest order. While holding 46 * either a block or index hash chain lock, a thread can acquire an 47 * mc_cache_bg_lock, which in turn can also acquire mb_cache_spinlock. 48 * 49 * Synchronization: 50 * 51 * Since both mb_cache_entry_get and mb_cache_entry_find scan the block and 52 * index hash chian, it needs to lock the corresponding hash chain. For each 53 * mb_cache_entry within the chain, it needs to lock the mb_cache_entry to 54 * prevent either any simultaneous release or free on the entry and also 55 * to serialize accesses to either the e_used or e_queued member of the entry. 56 * 57 * To avoid having a dangling reference to an already freed 58 * mb_cache_entry, an mb_cache_entry is only freed when it is not on a 59 * block hash chain and also no longer being referenced, both e_used, 60 * and e_queued are 0's. When an mb_cache_entry is explicitly freed it is 61 * first removed from a block hash chain. 62 */ 63 64 #include <linux/kernel.h> 65 #include <linux/module.h> 66 67 #include <linux/hash.h> 68 #include <linux/fs.h> 69 #include <linux/mm.h> 70 #include <linux/slab.h> 71 #include <linux/sched.h> 72 #include <linux/list_bl.h> 73 #include <linux/mbcache.h> 74 #include <linux/init.h> 75 #include <linux/blockgroup_lock.h> 76 77 #ifdef MB_CACHE_DEBUG 78 # define mb_debug(f...) do { \ 79 printk(KERN_DEBUG f); \ 80 printk("\n"); \ 81 } while (0) 82 #define mb_assert(c) do { if (!(c)) \ 83 printk(KERN_ERR "assertion " #c " failed\n"); \ 84 } while(0) 85 #else 86 # define mb_debug(f...) do { } while(0) 87 # define mb_assert(c) do { } while(0) 88 #endif 89 #define mb_error(f...) do { \ 90 printk(KERN_ERR f); \ 91 printk("\n"); \ 92 } while(0) 93 94 #define MB_CACHE_WRITER ((unsigned short)~0U >> 1) 95 96 #define MB_CACHE_ENTRY_LOCK_BITS __builtin_log2(NR_BG_LOCKS) 97 #define MB_CACHE_ENTRY_LOCK_INDEX(ce) \ 98 (hash_long((unsigned long)ce, MB_CACHE_ENTRY_LOCK_BITS)) 99 100 static DECLARE_WAIT_QUEUE_HEAD(mb_cache_queue); 101 static struct blockgroup_lock *mb_cache_bg_lock; 102 103 MODULE_AUTHOR("Andreas Gruenbacher <a.gruenbacher@computer.org>"); 104 MODULE_DESCRIPTION("Meta block cache (for extended attributes)"); 105 MODULE_LICENSE("GPL"); 106 107 EXPORT_SYMBOL(mb_cache_create); 108 EXPORT_SYMBOL(mb_cache_shrink); 109 EXPORT_SYMBOL(mb_cache_destroy); 110 EXPORT_SYMBOL(mb_cache_entry_alloc); 111 EXPORT_SYMBOL(mb_cache_entry_insert); 112 EXPORT_SYMBOL(mb_cache_entry_release); 113 EXPORT_SYMBOL(mb_cache_entry_free); 114 EXPORT_SYMBOL(mb_cache_entry_get); 115 #if !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0) 116 EXPORT_SYMBOL(mb_cache_entry_find_first); 117 EXPORT_SYMBOL(mb_cache_entry_find_next); 118 #endif 119 120 /* 121 * Global data: list of all mbcache's, lru list, and a spinlock for 122 * accessing cache data structures on SMP machines. The lru list is 123 * global across all mbcaches. 124 */ 125 126 static LIST_HEAD(mb_cache_list); 127 static LIST_HEAD(mb_cache_lru_list); 128 static DEFINE_SPINLOCK(mb_cache_spinlock); 129 130 static inline void 131 __spin_lock_mb_cache_entry(struct mb_cache_entry *ce) 132 { 133 spin_lock(bgl_lock_ptr(mb_cache_bg_lock, 134 MB_CACHE_ENTRY_LOCK_INDEX(ce))); 135 } 136 137 static inline void 138 __spin_unlock_mb_cache_entry(struct mb_cache_entry *ce) 139 { 140 spin_unlock(bgl_lock_ptr(mb_cache_bg_lock, 141 MB_CACHE_ENTRY_LOCK_INDEX(ce))); 142 } 143 144 static inline int 145 __mb_cache_entry_is_block_hashed(struct mb_cache_entry *ce) 146 { 147 return !hlist_bl_unhashed(&ce->e_block_list); 148 } 149 150 151 static inline void 152 __mb_cache_entry_unhash_block(struct mb_cache_entry *ce) 153 { 154 if (__mb_cache_entry_is_block_hashed(ce)) 155 hlist_bl_del_init(&ce->e_block_list); 156 } 157 158 static inline int 159 __mb_cache_entry_is_index_hashed(struct mb_cache_entry *ce) 160 { 161 return !hlist_bl_unhashed(&ce->e_index.o_list); 162 } 163 164 static inline void 165 __mb_cache_entry_unhash_index(struct mb_cache_entry *ce) 166 { 167 if (__mb_cache_entry_is_index_hashed(ce)) 168 hlist_bl_del_init(&ce->e_index.o_list); 169 } 170 171 /* 172 * __mb_cache_entry_unhash_unlock() 173 * 174 * This function is called to unhash both the block and index hash 175 * chain. 176 * It assumes both the block and index hash chain is locked upon entry. 177 * It also unlock both hash chains both exit 178 */ 179 static inline void 180 __mb_cache_entry_unhash_unlock(struct mb_cache_entry *ce) 181 { 182 __mb_cache_entry_unhash_index(ce); 183 hlist_bl_unlock(ce->e_index_hash_p); 184 __mb_cache_entry_unhash_block(ce); 185 hlist_bl_unlock(ce->e_block_hash_p); 186 } 187 188 static void 189 __mb_cache_entry_forget(struct mb_cache_entry *ce, gfp_t gfp_mask) 190 { 191 struct mb_cache *cache = ce->e_cache; 192 193 mb_assert(!(ce->e_used || ce->e_queued || atomic_read(&ce->e_refcnt))); 194 kmem_cache_free(cache->c_entry_cache, ce); 195 atomic_dec(&cache->c_entry_count); 196 } 197 198 static void 199 __mb_cache_entry_release(struct mb_cache_entry *ce) 200 { 201 /* First lock the entry to serialize access to its local data. */ 202 __spin_lock_mb_cache_entry(ce); 203 /* Wake up all processes queuing for this cache entry. */ 204 if (ce->e_queued) 205 wake_up_all(&mb_cache_queue); 206 if (ce->e_used >= MB_CACHE_WRITER) 207 ce->e_used -= MB_CACHE_WRITER; 208 /* 209 * Make sure that all cache entries on lru_list have 210 * both e_used and e_qued of 0s. 211 */ 212 ce->e_used--; 213 if (!(ce->e_used || ce->e_queued || atomic_read(&ce->e_refcnt))) { 214 if (!__mb_cache_entry_is_block_hashed(ce)) { 215 __spin_unlock_mb_cache_entry(ce); 216 goto forget; 217 } 218 /* 219 * Need access to lru list, first drop entry lock, 220 * then reacquire the lock in the proper order. 221 */ 222 spin_lock(&mb_cache_spinlock); 223 if (list_empty(&ce->e_lru_list)) 224 list_add_tail(&ce->e_lru_list, &mb_cache_lru_list); 225 spin_unlock(&mb_cache_spinlock); 226 } 227 __spin_unlock_mb_cache_entry(ce); 228 return; 229 forget: 230 mb_assert(list_empty(&ce->e_lru_list)); 231 __mb_cache_entry_forget(ce, GFP_KERNEL); 232 } 233 234 /* 235 * mb_cache_shrink_scan() memory pressure callback 236 * 237 * This function is called by the kernel memory management when memory 238 * gets low. 239 * 240 * @shrink: (ignored) 241 * @sc: shrink_control passed from reclaim 242 * 243 * Returns the number of objects freed. 244 */ 245 static unsigned long 246 mb_cache_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) 247 { 248 LIST_HEAD(free_list); 249 struct mb_cache_entry *entry, *tmp; 250 int nr_to_scan = sc->nr_to_scan; 251 gfp_t gfp_mask = sc->gfp_mask; 252 unsigned long freed = 0; 253 254 mb_debug("trying to free %d entries", nr_to_scan); 255 spin_lock(&mb_cache_spinlock); 256 while ((nr_to_scan-- > 0) && !list_empty(&mb_cache_lru_list)) { 257 struct mb_cache_entry *ce = 258 list_entry(mb_cache_lru_list.next, 259 struct mb_cache_entry, e_lru_list); 260 list_del_init(&ce->e_lru_list); 261 if (ce->e_used || ce->e_queued || atomic_read(&ce->e_refcnt)) 262 continue; 263 spin_unlock(&mb_cache_spinlock); 264 /* Prevent any find or get operation on the entry */ 265 hlist_bl_lock(ce->e_block_hash_p); 266 hlist_bl_lock(ce->e_index_hash_p); 267 /* Ignore if it is touched by a find/get */ 268 if (ce->e_used || ce->e_queued || atomic_read(&ce->e_refcnt) || 269 !list_empty(&ce->e_lru_list)) { 270 hlist_bl_unlock(ce->e_index_hash_p); 271 hlist_bl_unlock(ce->e_block_hash_p); 272 spin_lock(&mb_cache_spinlock); 273 continue; 274 } 275 __mb_cache_entry_unhash_unlock(ce); 276 list_add_tail(&ce->e_lru_list, &free_list); 277 spin_lock(&mb_cache_spinlock); 278 } 279 spin_unlock(&mb_cache_spinlock); 280 281 list_for_each_entry_safe(entry, tmp, &free_list, e_lru_list) { 282 __mb_cache_entry_forget(entry, gfp_mask); 283 freed++; 284 } 285 return freed; 286 } 287 288 static unsigned long 289 mb_cache_shrink_count(struct shrinker *shrink, struct shrink_control *sc) 290 { 291 struct mb_cache *cache; 292 unsigned long count = 0; 293 294 spin_lock(&mb_cache_spinlock); 295 list_for_each_entry(cache, &mb_cache_list, c_cache_list) { 296 mb_debug("cache %s (%d)", cache->c_name, 297 atomic_read(&cache->c_entry_count)); 298 count += atomic_read(&cache->c_entry_count); 299 } 300 spin_unlock(&mb_cache_spinlock); 301 302 return vfs_pressure_ratio(count); 303 } 304 305 static struct shrinker mb_cache_shrinker = { 306 .count_objects = mb_cache_shrink_count, 307 .scan_objects = mb_cache_shrink_scan, 308 .seeks = DEFAULT_SEEKS, 309 }; 310 311 /* 312 * mb_cache_create() create a new cache 313 * 314 * All entries in one cache are equal size. Cache entries may be from 315 * multiple devices. If this is the first mbcache created, registers 316 * the cache with kernel memory management. Returns NULL if no more 317 * memory was available. 318 * 319 * @name: name of the cache (informal) 320 * @bucket_bits: log2(number of hash buckets) 321 */ 322 struct mb_cache * 323 mb_cache_create(const char *name, int bucket_bits) 324 { 325 int n, bucket_count = 1 << bucket_bits; 326 struct mb_cache *cache = NULL; 327 328 if (!mb_cache_bg_lock) { 329 mb_cache_bg_lock = kmalloc(sizeof(struct blockgroup_lock), 330 GFP_KERNEL); 331 if (!mb_cache_bg_lock) 332 return NULL; 333 bgl_lock_init(mb_cache_bg_lock); 334 } 335 336 cache = kmalloc(sizeof(struct mb_cache), GFP_KERNEL); 337 if (!cache) 338 return NULL; 339 cache->c_name = name; 340 atomic_set(&cache->c_entry_count, 0); 341 cache->c_bucket_bits = bucket_bits; 342 cache->c_block_hash = kmalloc(bucket_count * 343 sizeof(struct hlist_bl_head), GFP_KERNEL); 344 if (!cache->c_block_hash) 345 goto fail; 346 for (n=0; n<bucket_count; n++) 347 INIT_HLIST_BL_HEAD(&cache->c_block_hash[n]); 348 cache->c_index_hash = kmalloc(bucket_count * 349 sizeof(struct hlist_bl_head), GFP_KERNEL); 350 if (!cache->c_index_hash) 351 goto fail; 352 for (n=0; n<bucket_count; n++) 353 INIT_HLIST_BL_HEAD(&cache->c_index_hash[n]); 354 cache->c_entry_cache = kmem_cache_create(name, 355 sizeof(struct mb_cache_entry), 0, 356 SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL); 357 if (!cache->c_entry_cache) 358 goto fail2; 359 360 /* 361 * Set an upper limit on the number of cache entries so that the hash 362 * chains won't grow too long. 363 */ 364 cache->c_max_entries = bucket_count << 4; 365 366 spin_lock(&mb_cache_spinlock); 367 list_add(&cache->c_cache_list, &mb_cache_list); 368 spin_unlock(&mb_cache_spinlock); 369 return cache; 370 371 fail2: 372 kfree(cache->c_index_hash); 373 374 fail: 375 kfree(cache->c_block_hash); 376 kfree(cache); 377 return NULL; 378 } 379 380 381 /* 382 * mb_cache_shrink() 383 * 384 * Removes all cache entries of a device from the cache. All cache entries 385 * currently in use cannot be freed, and thus remain in the cache. All others 386 * are freed. 387 * 388 * @bdev: which device's cache entries to shrink 389 */ 390 void 391 mb_cache_shrink(struct block_device *bdev) 392 { 393 LIST_HEAD(free_list); 394 struct list_head *l; 395 struct mb_cache_entry *ce, *tmp; 396 397 l = &mb_cache_lru_list; 398 spin_lock(&mb_cache_spinlock); 399 while (!list_is_last(l, &mb_cache_lru_list)) { 400 l = l->next; 401 ce = list_entry(l, struct mb_cache_entry, e_lru_list); 402 if (ce->e_bdev == bdev) { 403 list_del_init(&ce->e_lru_list); 404 if (ce->e_used || ce->e_queued || 405 atomic_read(&ce->e_refcnt)) 406 continue; 407 spin_unlock(&mb_cache_spinlock); 408 /* 409 * Prevent any find or get operation on the entry. 410 */ 411 hlist_bl_lock(ce->e_block_hash_p); 412 hlist_bl_lock(ce->e_index_hash_p); 413 /* Ignore if it is touched by a find/get */ 414 if (ce->e_used || ce->e_queued || 415 atomic_read(&ce->e_refcnt) || 416 !list_empty(&ce->e_lru_list)) { 417 hlist_bl_unlock(ce->e_index_hash_p); 418 hlist_bl_unlock(ce->e_block_hash_p); 419 l = &mb_cache_lru_list; 420 spin_lock(&mb_cache_spinlock); 421 continue; 422 } 423 __mb_cache_entry_unhash_unlock(ce); 424 mb_assert(!(ce->e_used || ce->e_queued || 425 atomic_read(&ce->e_refcnt))); 426 list_add_tail(&ce->e_lru_list, &free_list); 427 l = &mb_cache_lru_list; 428 spin_lock(&mb_cache_spinlock); 429 } 430 } 431 spin_unlock(&mb_cache_spinlock); 432 433 list_for_each_entry_safe(ce, tmp, &free_list, e_lru_list) { 434 __mb_cache_entry_forget(ce, GFP_KERNEL); 435 } 436 } 437 438 439 /* 440 * mb_cache_destroy() 441 * 442 * Shrinks the cache to its minimum possible size (hopefully 0 entries), 443 * and then destroys it. If this was the last mbcache, un-registers the 444 * mbcache from kernel memory management. 445 */ 446 void 447 mb_cache_destroy(struct mb_cache *cache) 448 { 449 LIST_HEAD(free_list); 450 struct mb_cache_entry *ce, *tmp; 451 452 spin_lock(&mb_cache_spinlock); 453 list_for_each_entry_safe(ce, tmp, &mb_cache_lru_list, e_lru_list) { 454 if (ce->e_cache == cache) 455 list_move_tail(&ce->e_lru_list, &free_list); 456 } 457 list_del(&cache->c_cache_list); 458 spin_unlock(&mb_cache_spinlock); 459 460 list_for_each_entry_safe(ce, tmp, &free_list, e_lru_list) { 461 list_del_init(&ce->e_lru_list); 462 /* 463 * Prevent any find or get operation on the entry. 464 */ 465 hlist_bl_lock(ce->e_block_hash_p); 466 hlist_bl_lock(ce->e_index_hash_p); 467 mb_assert(!(ce->e_used || ce->e_queued || 468 atomic_read(&ce->e_refcnt))); 469 __mb_cache_entry_unhash_unlock(ce); 470 __mb_cache_entry_forget(ce, GFP_KERNEL); 471 } 472 473 if (atomic_read(&cache->c_entry_count) > 0) { 474 mb_error("cache %s: %d orphaned entries", 475 cache->c_name, 476 atomic_read(&cache->c_entry_count)); 477 } 478 479 kfree(cache->c_index_hash); 480 kfree(cache->c_block_hash); 481 kfree(cache); 482 } 483 484 /* 485 * mb_cache_entry_alloc() 486 * 487 * Allocates a new cache entry. The new entry will not be valid initially, 488 * and thus cannot be looked up yet. It should be filled with data, and 489 * then inserted into the cache using mb_cache_entry_insert(). Returns NULL 490 * if no more memory was available. 491 */ 492 struct mb_cache_entry * 493 mb_cache_entry_alloc(struct mb_cache *cache, gfp_t gfp_flags) 494 { 495 struct mb_cache_entry *ce; 496 497 if (atomic_read(&cache->c_entry_count) >= cache->c_max_entries) { 498 struct list_head *l; 499 500 l = &mb_cache_lru_list; 501 spin_lock(&mb_cache_spinlock); 502 while (!list_is_last(l, &mb_cache_lru_list)) { 503 l = l->next; 504 ce = list_entry(l, struct mb_cache_entry, e_lru_list); 505 if (ce->e_cache == cache) { 506 list_del_init(&ce->e_lru_list); 507 if (ce->e_used || ce->e_queued || 508 atomic_read(&ce->e_refcnt)) 509 continue; 510 spin_unlock(&mb_cache_spinlock); 511 /* 512 * Prevent any find or get operation on the 513 * entry. 514 */ 515 hlist_bl_lock(ce->e_block_hash_p); 516 hlist_bl_lock(ce->e_index_hash_p); 517 /* Ignore if it is touched by a find/get */ 518 if (ce->e_used || ce->e_queued || 519 atomic_read(&ce->e_refcnt) || 520 !list_empty(&ce->e_lru_list)) { 521 hlist_bl_unlock(ce->e_index_hash_p); 522 hlist_bl_unlock(ce->e_block_hash_p); 523 l = &mb_cache_lru_list; 524 spin_lock(&mb_cache_spinlock); 525 continue; 526 } 527 mb_assert(list_empty(&ce->e_lru_list)); 528 mb_assert(!(ce->e_used || ce->e_queued || 529 atomic_read(&ce->e_refcnt))); 530 __mb_cache_entry_unhash_unlock(ce); 531 goto found; 532 } 533 } 534 spin_unlock(&mb_cache_spinlock); 535 } 536 537 ce = kmem_cache_alloc(cache->c_entry_cache, gfp_flags); 538 if (!ce) 539 return NULL; 540 atomic_inc(&cache->c_entry_count); 541 INIT_LIST_HEAD(&ce->e_lru_list); 542 INIT_HLIST_BL_NODE(&ce->e_block_list); 543 INIT_HLIST_BL_NODE(&ce->e_index.o_list); 544 ce->e_cache = cache; 545 ce->e_queued = 0; 546 atomic_set(&ce->e_refcnt, 0); 547 found: 548 ce->e_block_hash_p = &cache->c_block_hash[0]; 549 ce->e_index_hash_p = &cache->c_index_hash[0]; 550 ce->e_used = 1 + MB_CACHE_WRITER; 551 return ce; 552 } 553 554 555 /* 556 * mb_cache_entry_insert() 557 * 558 * Inserts an entry that was allocated using mb_cache_entry_alloc() into 559 * the cache. After this, the cache entry can be looked up, but is not yet 560 * in the lru list as the caller still holds a handle to it. Returns 0 on 561 * success, or -EBUSY if a cache entry for that device + inode exists 562 * already (this may happen after a failed lookup, but when another process 563 * has inserted the same cache entry in the meantime). 564 * 565 * @bdev: device the cache entry belongs to 566 * @block: block number 567 * @key: lookup key 568 */ 569 int 570 mb_cache_entry_insert(struct mb_cache_entry *ce, struct block_device *bdev, 571 sector_t block, unsigned int key) 572 { 573 struct mb_cache *cache = ce->e_cache; 574 unsigned int bucket; 575 struct hlist_bl_node *l; 576 struct hlist_bl_head *block_hash_p; 577 struct hlist_bl_head *index_hash_p; 578 struct mb_cache_entry *lce; 579 580 mb_assert(ce); 581 bucket = hash_long((unsigned long)bdev + (block & 0xffffffff), 582 cache->c_bucket_bits); 583 block_hash_p = &cache->c_block_hash[bucket]; 584 hlist_bl_lock(block_hash_p); 585 hlist_bl_for_each_entry(lce, l, block_hash_p, e_block_list) { 586 if (lce->e_bdev == bdev && lce->e_block == block) { 587 hlist_bl_unlock(block_hash_p); 588 return -EBUSY; 589 } 590 } 591 mb_assert(!__mb_cache_entry_is_block_hashed(ce)); 592 __mb_cache_entry_unhash_block(ce); 593 __mb_cache_entry_unhash_index(ce); 594 ce->e_bdev = bdev; 595 ce->e_block = block; 596 ce->e_block_hash_p = block_hash_p; 597 ce->e_index.o_key = key; 598 hlist_bl_add_head(&ce->e_block_list, block_hash_p); 599 hlist_bl_unlock(block_hash_p); 600 bucket = hash_long(key, cache->c_bucket_bits); 601 index_hash_p = &cache->c_index_hash[bucket]; 602 hlist_bl_lock(index_hash_p); 603 ce->e_index_hash_p = index_hash_p; 604 hlist_bl_add_head(&ce->e_index.o_list, index_hash_p); 605 hlist_bl_unlock(index_hash_p); 606 return 0; 607 } 608 609 610 /* 611 * mb_cache_entry_release() 612 * 613 * Release a handle to a cache entry. When the last handle to a cache entry 614 * is released it is either freed (if it is invalid) or otherwise inserted 615 * in to the lru list. 616 */ 617 void 618 mb_cache_entry_release(struct mb_cache_entry *ce) 619 { 620 __mb_cache_entry_release(ce); 621 } 622 623 624 /* 625 * mb_cache_entry_free() 626 * 627 */ 628 void 629 mb_cache_entry_free(struct mb_cache_entry *ce) 630 { 631 mb_assert(ce); 632 mb_assert(list_empty(&ce->e_lru_list)); 633 hlist_bl_lock(ce->e_index_hash_p); 634 __mb_cache_entry_unhash_index(ce); 635 hlist_bl_unlock(ce->e_index_hash_p); 636 hlist_bl_lock(ce->e_block_hash_p); 637 __mb_cache_entry_unhash_block(ce); 638 hlist_bl_unlock(ce->e_block_hash_p); 639 __mb_cache_entry_release(ce); 640 } 641 642 643 /* 644 * mb_cache_entry_get() 645 * 646 * Get a cache entry by device / block number. (There can only be one entry 647 * in the cache per device and block.) Returns NULL if no such cache entry 648 * exists. The returned cache entry is locked for exclusive access ("single 649 * writer"). 650 */ 651 struct mb_cache_entry * 652 mb_cache_entry_get(struct mb_cache *cache, struct block_device *bdev, 653 sector_t block) 654 { 655 unsigned int bucket; 656 struct hlist_bl_node *l; 657 struct mb_cache_entry *ce; 658 struct hlist_bl_head *block_hash_p; 659 660 bucket = hash_long((unsigned long)bdev + (block & 0xffffffff), 661 cache->c_bucket_bits); 662 block_hash_p = &cache->c_block_hash[bucket]; 663 /* First serialize access to the block corresponding hash chain. */ 664 hlist_bl_lock(block_hash_p); 665 hlist_bl_for_each_entry(ce, l, block_hash_p, e_block_list) { 666 mb_assert(ce->e_block_hash_p == block_hash_p); 667 if (ce->e_bdev == bdev && ce->e_block == block) { 668 /* 669 * Prevent a free from removing the entry. 670 */ 671 atomic_inc(&ce->e_refcnt); 672 hlist_bl_unlock(block_hash_p); 673 __spin_lock_mb_cache_entry(ce); 674 atomic_dec(&ce->e_refcnt); 675 if (ce->e_used > 0) { 676 DEFINE_WAIT(wait); 677 while (ce->e_used > 0) { 678 ce->e_queued++; 679 prepare_to_wait(&mb_cache_queue, &wait, 680 TASK_UNINTERRUPTIBLE); 681 __spin_unlock_mb_cache_entry(ce); 682 schedule(); 683 __spin_lock_mb_cache_entry(ce); 684 ce->e_queued--; 685 } 686 finish_wait(&mb_cache_queue, &wait); 687 } 688 ce->e_used += 1 + MB_CACHE_WRITER; 689 __spin_unlock_mb_cache_entry(ce); 690 691 if (!list_empty(&ce->e_lru_list)) { 692 spin_lock(&mb_cache_spinlock); 693 list_del_init(&ce->e_lru_list); 694 spin_unlock(&mb_cache_spinlock); 695 } 696 if (!__mb_cache_entry_is_block_hashed(ce)) { 697 __mb_cache_entry_release(ce); 698 return NULL; 699 } 700 return ce; 701 } 702 } 703 hlist_bl_unlock(block_hash_p); 704 return NULL; 705 } 706 707 #if !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0) 708 709 static struct mb_cache_entry * 710 __mb_cache_entry_find(struct hlist_bl_node *l, struct hlist_bl_head *head, 711 struct block_device *bdev, unsigned int key) 712 { 713 714 /* The index hash chain is alredy acquire by caller. */ 715 while (l != NULL) { 716 struct mb_cache_entry *ce = 717 hlist_bl_entry(l, struct mb_cache_entry, 718 e_index.o_list); 719 mb_assert(ce->e_index_hash_p == head); 720 if (ce->e_bdev == bdev && ce->e_index.o_key == key) { 721 /* 722 * Prevent a free from removing the entry. 723 */ 724 atomic_inc(&ce->e_refcnt); 725 hlist_bl_unlock(head); 726 __spin_lock_mb_cache_entry(ce); 727 atomic_dec(&ce->e_refcnt); 728 ce->e_used++; 729 /* Incrementing before holding the lock gives readers 730 priority over writers. */ 731 if (ce->e_used >= MB_CACHE_WRITER) { 732 DEFINE_WAIT(wait); 733 734 while (ce->e_used >= MB_CACHE_WRITER) { 735 ce->e_queued++; 736 prepare_to_wait(&mb_cache_queue, &wait, 737 TASK_UNINTERRUPTIBLE); 738 __spin_unlock_mb_cache_entry(ce); 739 schedule(); 740 __spin_lock_mb_cache_entry(ce); 741 ce->e_queued--; 742 } 743 finish_wait(&mb_cache_queue, &wait); 744 } 745 __spin_unlock_mb_cache_entry(ce); 746 if (!list_empty(&ce->e_lru_list)) { 747 spin_lock(&mb_cache_spinlock); 748 list_del_init(&ce->e_lru_list); 749 spin_unlock(&mb_cache_spinlock); 750 } 751 if (!__mb_cache_entry_is_block_hashed(ce)) { 752 __mb_cache_entry_release(ce); 753 return ERR_PTR(-EAGAIN); 754 } 755 return ce; 756 } 757 l = l->next; 758 } 759 hlist_bl_unlock(head); 760 return NULL; 761 } 762 763 764 /* 765 * mb_cache_entry_find_first() 766 * 767 * Find the first cache entry on a given device with a certain key in 768 * an additional index. Additional matches can be found with 769 * mb_cache_entry_find_next(). Returns NULL if no match was found. The 770 * returned cache entry is locked for shared access ("multiple readers"). 771 * 772 * @cache: the cache to search 773 * @bdev: the device the cache entry should belong to 774 * @key: the key in the index 775 */ 776 struct mb_cache_entry * 777 mb_cache_entry_find_first(struct mb_cache *cache, struct block_device *bdev, 778 unsigned int key) 779 { 780 unsigned int bucket = hash_long(key, cache->c_bucket_bits); 781 struct hlist_bl_node *l; 782 struct mb_cache_entry *ce = NULL; 783 struct hlist_bl_head *index_hash_p; 784 785 index_hash_p = &cache->c_index_hash[bucket]; 786 hlist_bl_lock(index_hash_p); 787 if (!hlist_bl_empty(index_hash_p)) { 788 l = hlist_bl_first(index_hash_p); 789 ce = __mb_cache_entry_find(l, index_hash_p, bdev, key); 790 } else 791 hlist_bl_unlock(index_hash_p); 792 return ce; 793 } 794 795 796 /* 797 * mb_cache_entry_find_next() 798 * 799 * Find the next cache entry on a given device with a certain key in an 800 * additional index. Returns NULL if no match could be found. The previous 801 * entry is atomatically released, so that mb_cache_entry_find_next() can 802 * be called like this: 803 * 804 * entry = mb_cache_entry_find_first(); 805 * while (entry) { 806 * ... 807 * entry = mb_cache_entry_find_next(entry, ...); 808 * } 809 * 810 * @prev: The previous match 811 * @bdev: the device the cache entry should belong to 812 * @key: the key in the index 813 */ 814 struct mb_cache_entry * 815 mb_cache_entry_find_next(struct mb_cache_entry *prev, 816 struct block_device *bdev, unsigned int key) 817 { 818 struct mb_cache *cache = prev->e_cache; 819 unsigned int bucket = hash_long(key, cache->c_bucket_bits); 820 struct hlist_bl_node *l; 821 struct mb_cache_entry *ce; 822 struct hlist_bl_head *index_hash_p; 823 824 index_hash_p = &cache->c_index_hash[bucket]; 825 mb_assert(prev->e_index_hash_p == index_hash_p); 826 hlist_bl_lock(index_hash_p); 827 mb_assert(!hlist_bl_empty(index_hash_p)); 828 l = prev->e_index.o_list.next; 829 ce = __mb_cache_entry_find(l, index_hash_p, bdev, key); 830 __mb_cache_entry_release(prev); 831 return ce; 832 } 833 834 #endif /* !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0) */ 835 836 static int __init init_mbcache(void) 837 { 838 register_shrinker(&mb_cache_shrinker); 839 return 0; 840 } 841 842 static void __exit exit_mbcache(void) 843 { 844 unregister_shrinker(&mb_cache_shrinker); 845 } 846 847 module_init(init_mbcache) 848 module_exit(exit_mbcache) 849 850