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