fs/mbcache.c

   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 #include <linux/kernel.h>
  30 #include <linux/module.h>
  31
  32 #include <linux/hash.h>
  33 #include <linux/fs.h>
  34 #include <linux/mm.h>
  35 #include <linux/slab.h>
  36 #include <linux/sched.h>
  37 #include <linux/init.h>
  38 #include <linux/mbcache.h>
  39
  40
  41 #ifdef MB_CACHE_DEBUG
  42 # define mb_debug(f...) do { \
  43                 printk(KERN_DEBUG f); \
  44                 printk("\n"); \
  45         } while (0)
  46 #define mb_assert(c) do { if (!(c)) \
  47                 printk(KERN_ERR "assertion " #c " failed\n"); \
  48         } while(0)
  49 #else
  50 # define mb_debug(f...) do { } while(0)
  51 # define mb_assert(c) do { } while(0)
  52 #endif
  53 #define mb_error(f...) do { \
  54                 printk(KERN_ERR f); \
  55                 printk("\n"); \
  56         } while(0)
  57
  58 #define MB_CACHE_WRITER ((unsigned short)~0U >> 1)
  59
  60 static DECLARE_WAIT_QUEUE_HEAD(mb_cache_queue);
  61
  62 MODULE_AUTHOR("Andreas Gruenbacher <a.gruenbacher@computer.org>");
  63 MODULE_DESCRIPTION("Meta block cache (for extended attributes)");
  64 MODULE_LICENSE("GPL");
  65
  66 EXPORT_SYMBOL(mb_cache_create);
  67 EXPORT_SYMBOL(mb_cache_shrink);
  68 EXPORT_SYMBOL(mb_cache_destroy);
  69 EXPORT_SYMBOL(mb_cache_entry_alloc);
  70 EXPORT_SYMBOL(mb_cache_entry_insert);
  71 EXPORT_SYMBOL(mb_cache_entry_release);
  72 EXPORT_SYMBOL(mb_cache_entry_free);
  73 EXPORT_SYMBOL(mb_cache_entry_get);
  74 #if !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0)
  75 EXPORT_SYMBOL(mb_cache_entry_find_first);
  76 EXPORT_SYMBOL(mb_cache_entry_find_next);
  77 #endif
  78
  79 /*
  80  * Global data: list of all mbcache's, lru list, and a spinlock for
  81  * accessing cache data structures on SMP machines. The lru list is
  82  * global across all mbcaches.
  83  */
  84
  85 static LIST_HEAD(mb_cache_list);
  86 static LIST_HEAD(mb_cache_lru_list);
  87 static DEFINE_SPINLOCK(mb_cache_spinlock);
  88
  89 /*
  90  * What the mbcache registers as to get shrunk dynamically.
  91  */
  92
  93 static int mb_cache_shrink_fn(struct shrinker *shrink,
  94                               struct shrink_control *sc);
  95
  96 static struct shrinker mb_cache_shrinker = {
  97         .shrink = mb_cache_shrink_fn,
  98         .seeks = DEFAULT_SEEKS,
  99 };
 100
 101 static inline int
 102 __mb_cache_entry_is_hashed(struct mb_cache_entry *ce)
 103 {
 104         return !list_empty(&ce->e_block_list);
 105 }
 106
 107
 108 static void
 109 __mb_cache_entry_unhash(struct mb_cache_entry *ce)
 110 {
 111         if (__mb_cache_entry_is_hashed(ce)) {
 112                 list_del_init(&ce->e_block_list);
 113                 list_del(&ce->e_index.o_list);
 114         }
 115 }
 116
 117
 118 static void
 119 __mb_cache_entry_forget(struct mb_cache_entry *ce, gfp_t gfp_mask)
 120 {
 121         struct mb_cache *cache = ce->e_cache;
 122
 123         mb_assert(!(ce->e_used || ce->e_queued));
 124         kmem_cache_free(cache->c_entry_cache, ce);
 125         atomic_dec(&cache->c_entry_count);
 126 }
 127
 128
 129 static void
 130 __mb_cache_entry_release_unlock(struct mb_cache_entry *ce)
 131         __releases(mb_cache_spinlock)
 132 {
 133         /* Wake up all processes queuing for this cache entry. */
 134         if (ce->e_queued)
 135                 wake_up_all(&mb_cache_queue);
 136         if (ce->e_used >= MB_CACHE_WRITER)
 137                 ce->e_used -= MB_CACHE_WRITER;
 138         ce->e_used--;
 139         if (!(ce->e_used || ce->e_queued)) {
 140                 if (!__mb_cache_entry_is_hashed(ce))
 141                         goto forget;
 142                 mb_assert(list_empty(&ce->e_lru_list));
 143                 list_add_tail(&ce->e_lru_list, &mb_cache_lru_list);
 144         }
 145         spin_unlock(&mb_cache_spinlock);
 146         return;
 147 forget:
 148         spin_unlock(&mb_cache_spinlock);
 149         __mb_cache_entry_forget(ce, GFP_KERNEL);
 150 }
 151
 152
 153 /*
 154  * mb_cache_shrink_fn()  memory pressure callback
 155  *
 156  * This function is called by the kernel memory management when memory
 157  * gets low.
 158  *
 159  * @shrink: (ignored)
 160  * @sc: shrink_control passed from reclaim
 161  *
 162  * Returns the number of objects which are present in the cache.
 163  */
 164 static int
 165 mb_cache_shrink_fn(struct shrinker *shrink, struct shrink_control *sc)
 166 {
 167         LIST_HEAD(free_list);
 168         struct mb_cache *cache;
 169         struct mb_cache_entry *entry, *tmp;
 170         int count = 0;
 171         int nr_to_scan = sc->nr_to_scan;
 172         gfp_t gfp_mask = sc->gfp_mask;
 173
 174         mb_debug("trying to free %d entries", nr_to_scan);
 175         spin_lock(&mb_cache_spinlock);
 176         while (nr_to_scan-- && !list_empty(&mb_cache_lru_list)) {
 177                 struct mb_cache_entry *ce =
 178                         list_entry(mb_cache_lru_list.next,
 179                                    struct mb_cache_entry, e_lru_list);
 180                 list_move_tail(&ce->e_lru_list, &free_list);
 181                 __mb_cache_entry_unhash(ce);
 182         }
 183         list_for_each_entry(cache, &mb_cache_list, c_cache_list) {
 184                 mb_debug("cache %s (%d)", cache->c_name,
 185                           atomic_read(&cache->c_entry_count));
 186                 count += atomic_read(&cache->c_entry_count);
 187         }
 188         spin_unlock(&mb_cache_spinlock);
 189         list_for_each_entry_safe(entry, tmp, &free_list, e_lru_list) {
 190                 __mb_cache_entry_forget(entry, gfp_mask);
 191         }
 192         return (count / 100) * sysctl_vfs_cache_pressure;
 193 }
 194
 195
 196 /*
 197  * mb_cache_create()  create a new cache
 198  *
 199  * All entries in one cache are equal size. Cache entries may be from
 200  * multiple devices. If this is the first mbcache created, registers
 201  * the cache with kernel memory management. Returns NULL if no more
 202  * memory was available.
 203  *
 204  * @name: name of the cache (informal)
 205  * @bucket_bits: log2(number of hash buckets)
 206  */
 207 struct mb_cache *
 208 mb_cache_create(const char *name, int bucket_bits)
 209 {
 210         int n, bucket_count = 1 << bucket_bits;
 211         struct mb_cache *cache = NULL;
 212
 213         cache = kmalloc(sizeof(struct mb_cache), GFP_KERNEL);
 214         if (!cache)
 215                 return NULL;
 216         cache->c_name = name;
 217         atomic_set(&cache->c_entry_count, 0);
 218         cache->c_bucket_bits = bucket_bits;
 219         cache->c_block_hash = kmalloc(bucket_count * sizeof(struct list_head),
 220                                       GFP_KERNEL);
 221         if (!cache->c_block_hash)
 222                 goto fail;
 223         for (n=0; n<bucket_count; n++)
 224                 INIT_LIST_HEAD(&cache->c_block_hash[n]);
 225         cache->c_index_hash = kmalloc(bucket_count * sizeof(struct list_head),
 226                                       GFP_KERNEL);
 227         if (!cache->c_index_hash)
 228                 goto fail;
 229         for (n=0; n<bucket_count; n++)
 230                 INIT_LIST_HEAD(&cache->c_index_hash[n]);
 231         cache->c_entry_cache = kmem_cache_create(name,
 232                 sizeof(struct mb_cache_entry), 0,
 233                 SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL);
 234         if (!cache->c_entry_cache)
 235                 goto fail2;
 236
 237         /*
 238          * Set an upper limit on the number of cache entries so that the hash
 239          * chains won't grow too long.
 240          */
 241         cache->c_max_entries = bucket_count << 4;
 242
 243         spin_lock(&mb_cache_spinlock);
 244         list_add(&cache->c_cache_list, &mb_cache_list);
 245         spin_unlock(&mb_cache_spinlock);
 246         return cache;
 247
 248 fail2:
 249         kfree(cache->c_index_hash);
 250
 251 fail:
 252         kfree(cache->c_block_hash);
 253         kfree(cache);
 254         return NULL;
 255 }
 256
 257
 258 /*
 259  * mb_cache_shrink()
 260  *
 261  * Removes all cache entries of a device from the cache. All cache entries
 262  * currently in use cannot be freed, and thus remain in the cache. All others
 263  * are freed.
 264  *
 265  * @bdev: which device's cache entries to shrink
 266  */
 267 void
 268 mb_cache_shrink(struct block_device *bdev)
 269 {
 270         LIST_HEAD(free_list);
 271         struct list_head *l, *ltmp;
 272
 273         spin_lock(&mb_cache_spinlock);
 274         list_for_each_safe(l, ltmp, &mb_cache_lru_list) {
 275                 struct mb_cache_entry *ce =
 276                         list_entry(l, struct mb_cache_entry, e_lru_list);
 277                 if (ce->e_bdev == bdev) {
 278                         list_move_tail(&ce->e_lru_list, &free_list);
 279                         __mb_cache_entry_unhash(ce);
 280                 }
 281         }
 282         spin_unlock(&mb_cache_spinlock);
 283         list_for_each_safe(l, ltmp, &free_list) {
 284                 __mb_cache_entry_forget(list_entry(l, struct mb_cache_entry,
 285                                                    e_lru_list), GFP_KERNEL);
 286         }
 287 }
 288
 289
 290 /*
 291  * mb_cache_destroy()
 292  *
 293  * Shrinks the cache to its minimum possible size (hopefully 0 entries),
 294  * and then destroys it. If this was the last mbcache, un-registers the
 295  * mbcache from kernel memory management.
 296  */
 297 void
 298 mb_cache_destroy(struct mb_cache *cache)
 299 {
 300         LIST_HEAD(free_list);
 301         struct list_head *l, *ltmp;
 302
 303         spin_lock(&mb_cache_spinlock);
 304         list_for_each_safe(l, ltmp, &mb_cache_lru_list) {
 305                 struct mb_cache_entry *ce =
 306                         list_entry(l, struct mb_cache_entry, e_lru_list);
 307                 if (ce->e_cache == cache) {
 308                         list_move_tail(&ce->e_lru_list, &free_list);
 309                         __mb_cache_entry_unhash(ce);
 310                 }
 311         }
 312         list_del(&cache->c_cache_list);
 313         spin_unlock(&mb_cache_spinlock);
 314
 315         list_for_each_safe(l, ltmp, &free_list) {
 316                 __mb_cache_entry_forget(list_entry(l, struct mb_cache_entry,
 317                                                    e_lru_list), GFP_KERNEL);
 318         }
 319
 320         if (atomic_read(&cache->c_entry_count) > 0) {
 321                 mb_error("cache %s: %d orphaned entries",
 322                           cache->c_name,
 323                           atomic_read(&cache->c_entry_count));
 324         }
 325
 326         kmem_cache_destroy(cache->c_entry_cache);
 327
 328         kfree(cache->c_index_hash);
 329         kfree(cache->c_block_hash);
 330         kfree(cache);
 331 }
 332
 333 /*
 334  * mb_cache_entry_alloc()
 335  *
 336  * Allocates a new cache entry. The new entry will not be valid initially,
 337  * and thus cannot be looked up yet. It should be filled with data, and
 338  * then inserted into the cache using mb_cache_entry_insert(). Returns NULL
 339  * if no more memory was available.
 340  */
 341 struct mb_cache_entry *
 342 mb_cache_entry_alloc(struct mb_cache *cache, gfp_t gfp_flags)
 343 {
 344         struct mb_cache_entry *ce = NULL;
 345
 346         if (atomic_read(&cache->c_entry_count) >= cache->c_max_entries) {
 347                 spin_lock(&mb_cache_spinlock);
 348                 if (!list_empty(&mb_cache_lru_list)) {
 349                         ce = list_entry(mb_cache_lru_list.next,
 350                                         struct mb_cache_entry, e_lru_list);
 351                         list_del_init(&ce->e_lru_list);
 352                         __mb_cache_entry_unhash(ce);
 353                 }
 354                 spin_unlock(&mb_cache_spinlock);
 355         }
 356         if (!ce) {
 357                 ce = kmem_cache_alloc(cache->c_entry_cache, gfp_flags);
 358                 if (!ce)
 359                         return NULL;
 360                 atomic_inc(&cache->c_entry_count);
 361                 INIT_LIST_HEAD(&ce->e_lru_list);
 362                 INIT_LIST_HEAD(&ce->e_block_list);
 363                 ce->e_cache = cache;
 364                 ce->e_queued = 0;
 365         }
 366         ce->e_used = 1 + MB_CACHE_WRITER;
 367         return ce;
 368 }
 369
 370
 371 /*
 372  * mb_cache_entry_insert()
 373  *
 374  * Inserts an entry that was allocated using mb_cache_entry_alloc() into
 375  * the cache. After this, the cache entry can be looked up, but is not yet
 376  * in the lru list as the caller still holds a handle to it. Returns 0 on
 377  * success, or -EBUSY if a cache entry for that device + inode exists
 378  * already (this may happen after a failed lookup, but when another process
 379  * has inserted the same cache entry in the meantime).
 380  *
 381  * @bdev: device the cache entry belongs to
 382  * @block: block number
 383  * @key: lookup key
 384  */
 385 int
 386 mb_cache_entry_insert(struct mb_cache_entry *ce, struct block_device *bdev,
 387                       sector_t block, unsigned int key)
 388 {
 389         struct mb_cache *cache = ce->e_cache;
 390         unsigned int bucket;
 391         struct list_head *l;
 392         int error = -EBUSY;
 393
 394         bucket = hash_long((unsigned long)bdev + (block & 0xffffffff),
 395                            cache->c_bucket_bits);
 396         spin_lock(&mb_cache_spinlock);
 397         list_for_each_prev(l, &cache->c_block_hash[bucket]) {
 398                 struct mb_cache_entry *ce =
 399                         list_entry(l, struct mb_cache_entry, e_block_list);
 400                 if (ce->e_bdev == bdev && ce->e_block == block)
 401                         goto out;
 402         }
 403         __mb_cache_entry_unhash(ce);
 404         ce->e_bdev = bdev;
 405         ce->e_block = block;
 406         list_add(&ce->e_block_list, &cache->c_block_hash[bucket]);
 407         ce->e_index.o_key = key;
 408         bucket = hash_long(key, cache->c_bucket_bits);
 409         list_add(&ce->e_index.o_list, &cache->c_index_hash[bucket]);
 410         error = 0;
 411 out:
 412         spin_unlock(&mb_cache_spinlock);
 413         return error;
 414 }
 415
 416
 417 /*
 418  * mb_cache_entry_release()
 419  *
 420  * Release a handle to a cache entry. When the last handle to a cache entry
 421  * is released it is either freed (if it is invalid) or otherwise inserted
 422  * in to the lru list.
 423  */
 424 void
 425 mb_cache_entry_release(struct mb_cache_entry *ce)
 426 {
 427         spin_lock(&mb_cache_spinlock);
 428         __mb_cache_entry_release_unlock(ce);
 429 }
 430
 431
 432 /*
 433  * mb_cache_entry_free()
 434  *
 435  * This is equivalent to the sequence mb_cache_entry_takeout() --
 436  * mb_cache_entry_release().
 437  */
 438 void
 439 mb_cache_entry_free(struct mb_cache_entry *ce)
 440 {
 441         spin_lock(&mb_cache_spinlock);
 442         mb_assert(list_empty(&ce->e_lru_list));
 443         __mb_cache_entry_unhash(ce);
 444         __mb_cache_entry_release_unlock(ce);
 445 }
 446
 447
 448 /*
 449  * mb_cache_entry_get()
 450  *
 451  * Get a cache entry  by device / block number. (There can only be one entry
 452  * in the cache per device and block.) Returns NULL if no such cache entry
 453  * exists. The returned cache entry is locked for exclusive access ("single
 454  * writer").
 455  */
 456 struct mb_cache_entry *
 457 mb_cache_entry_get(struct mb_cache *cache, struct block_device *bdev,
 458                    sector_t block)
 459 {
 460         unsigned int bucket;
 461         struct list_head *l;
 462         struct mb_cache_entry *ce;
 463
 464         bucket = hash_long((unsigned long)bdev + (block & 0xffffffff),
 465                            cache->c_bucket_bits);
 466         spin_lock(&mb_cache_spinlock);
 467         list_for_each(l, &cache->c_block_hash[bucket]) {
 468                 ce = list_entry(l, struct mb_cache_entry, e_block_list);
 469                 if (ce->e_bdev == bdev && ce->e_block == block) {
 470                         DEFINE_WAIT(wait);
 471
 472                         if (!list_empty(&ce->e_lru_list))
 473                                 list_del_init(&ce->e_lru_list);
 474
 475                         while (ce->e_used > 0) {
 476                                 ce->e_queued++;
 477                                 prepare_to_wait(&mb_cache_queue, &wait,
 478                                                 TASK_UNINTERRUPTIBLE);
 479                                 spin_unlock(&mb_cache_spinlock);
 480                                 schedule();
 481                                 spin_lock(&mb_cache_spinlock);
 482                                 ce->e_queued--;
 483                         }
 484                         finish_wait(&mb_cache_queue, &wait);
 485                         ce->e_used += 1 + MB_CACHE_WRITER;
 486
 487                         if (!__mb_cache_entry_is_hashed(ce)) {
 488                                 __mb_cache_entry_release_unlock(ce);
 489                                 return NULL;
 490                         }
 491                         goto cleanup;
 492                 }
 493         }
 494         ce = NULL;
 495
 496 cleanup:
 497         spin_unlock(&mb_cache_spinlock);
 498         return ce;
 499 }
 500
 501 #if !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0)
 502
 503 static struct mb_cache_entry *
 504 __mb_cache_entry_find(struct list_head *l, struct list_head *head,
 505                       struct block_device *bdev, unsigned int key)
 506 {
 507         while (l != head) {
 508                 struct mb_cache_entry *ce =
 509                         list_entry(l, struct mb_cache_entry, e_index.o_list);
 510                 if (ce->e_bdev == bdev && ce->e_index.o_key == key) {
 511                         DEFINE_WAIT(wait);
 512
 513                         if (!list_empty(&ce->e_lru_list))
 514                                 list_del_init(&ce->e_lru_list);
 515
 516                         /* Incrementing before holding the lock gives readers
 517                            priority over writers. */
 518                         ce->e_used++;
 519                         while (ce->e_used >= MB_CACHE_WRITER) {
 520                                 ce->e_queued++;
 521                                 prepare_to_wait(&mb_cache_queue, &wait,
 522                                                 TASK_UNINTERRUPTIBLE);
 523                                 spin_unlock(&mb_cache_spinlock);
 524                                 schedule();
 525                                 spin_lock(&mb_cache_spinlock);
 526                                 ce->e_queued--;
 527                         }
 528                         finish_wait(&mb_cache_queue, &wait);
 529
 530                         if (!__mb_cache_entry_is_hashed(ce)) {
 531                                 __mb_cache_entry_release_unlock(ce);
 532                                 spin_lock(&mb_cache_spinlock);
 533                                 return ERR_PTR(-EAGAIN);
 534                         }
 535                         return ce;
 536                 }
 537                 l = l->next;
 538         }
 539         return NULL;
 540 }
 541
 542
 543 /*
 544  * mb_cache_entry_find_first()
 545  *
 546  * Find the first cache entry on a given device with a certain key in
 547  * an additional index. Additional matches can be found with
 548  * mb_cache_entry_find_next(). Returns NULL if no match was found. The
 549  * returned cache entry is locked for shared access ("multiple readers").
 550  *
 551  * @cache: the cache to search
 552  * @bdev: the device the cache entry should belong to
 553  * @key: the key in the index
 554  */
 555 struct mb_cache_entry *
 556 mb_cache_entry_find_first(struct mb_cache *cache, struct block_device *bdev,
 557                           unsigned int key)
 558 {
 559         unsigned int bucket = hash_long(key, cache->c_bucket_bits);
 560         struct list_head *l;
 561         struct mb_cache_entry *ce;
 562
 563         spin_lock(&mb_cache_spinlock);
 564         l = cache->c_index_hash[bucket].next;
 565         ce = __mb_cache_entry_find(l, &cache->c_index_hash[bucket], bdev, key);
 566         spin_unlock(&mb_cache_spinlock);
 567         return ce;
 568 }
 569
 570
 571 /*
 572  * mb_cache_entry_find_next()
 573  *
 574  * Find the next cache entry on a given device with a certain key in an
 575  * additional index. Returns NULL if no match could be found. The previous
 576  * entry is atomatically released, so that mb_cache_entry_find_next() can
 577  * be called like this:
 578  *
 579  * entry = mb_cache_entry_find_first();
 580  * while (entry) {
 581  *      ...
 582  *      entry = mb_cache_entry_find_next(entry, ...);
 583  * }
 584  *
 585  * @prev: The previous match
 586  * @bdev: the device the cache entry should belong to
 587  * @key: the key in the index
 588  */
 589 struct mb_cache_entry *
 590 mb_cache_entry_find_next(struct mb_cache_entry *prev,
 591                          struct block_device *bdev, unsigned int key)
 592 {
 593         struct mb_cache *cache = prev->e_cache;
 594         unsigned int bucket = hash_long(key, cache->c_bucket_bits);
 595         struct list_head *l;
 596         struct mb_cache_entry *ce;
 597
 598         spin_lock(&mb_cache_spinlock);
 599         l = prev->e_index.o_list.next;
 600         ce = __mb_cache_entry_find(l, &cache->c_index_hash[bucket], bdev, key);
 601         __mb_cache_entry_release_unlock(prev);
 602         return ce;
 603 }
 604
 605 #endif  /* !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0) */
 606
 607 static int __init init_mbcache(void)
 608 {
 609         register_shrinker(&mb_cache_shrinker);
 610         return 0;
 611 }
 612
 613 static void __exit exit_mbcache(void)
 614 {
 615         unregister_shrinker(&mb_cache_shrinker);
 616 }
 617
 618 module_init(init_mbcache)
 619 module_exit(exit_mbcache)
 620