projects/linux·blob v3.13 · refs

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1/*
2 * linux/fs/mbcache.c
3 * (C) 2001-2002 Andreas Gruenbacher, <[email protected]>
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 <[email protected]>");
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
89static inline int
90__mb_cache_entry_is_hashed(struct mb_cache_entry *ce)
91{
92 return !list_empty(&ce->e_block_list);
93}
94
95
96static void
97__mb_cache_entry_unhash(struct mb_cache_entry *ce)
98{
99 if (__mb_cache_entry_is_hashed(ce)) {
100 list_del_init(&ce->e_block_list);
101 list_del(&ce->e_index.o_list);
102 }
103}
104
105
106static void
107__mb_cache_entry_forget(struct mb_cache_entry *ce, gfp_t gfp_mask)
108{
109 struct mb_cache *cache = ce->e_cache;
110
111 mb_assert(!(ce->e_used || ce->e_queued));
112 kmem_cache_free(cache->c_entry_cache, ce);
113 atomic_dec(&cache->c_entry_count);
114}
115
116
117static void
118__mb_cache_entry_release_unlock(struct mb_cache_entry *ce)
119 __releases(mb_cache_spinlock)
120{
121 /* Wake up all processes queuing for this cache entry. */
122 if (ce->e_queued)
123 wake_up_all(&mb_cache_queue);
124 if (ce->e_used >= MB_CACHE_WRITER)
125 ce->e_used -= MB_CACHE_WRITER;
126 ce->e_used--;
127 if (!(ce->e_used || ce->e_queued)) {
128 if (!__mb_cache_entry_is_hashed(ce))
129 goto forget;
130 mb_assert(list_empty(&ce->e_lru_list));
131 list_add_tail(&ce->e_lru_list, &mb_cache_lru_list);
132 }
133 spin_unlock(&mb_cache_spinlock);
134 return;
135forget:
136 spin_unlock(&mb_cache_spinlock);
137 __mb_cache_entry_forget(ce, GFP_KERNEL);
138}
139
140
141/*
142 * mb_cache_shrink_scan() memory pressure callback
143 *
144 * This function is called by the kernel memory management when memory
145 * gets low.
146 *
147 * @shrink: (ignored)
148 * @sc: shrink_control passed from reclaim
149 *
150 * Returns the number of objects freed.
151 */
152static unsigned long
153mb_cache_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
154{
155 LIST_HEAD(free_list);
156 struct mb_cache_entry *entry, *tmp;
157 int nr_to_scan = sc->nr_to_scan;
158 gfp_t gfp_mask = sc->gfp_mask;
159 unsigned long freed = 0;
160
161 mb_debug("trying to free %d entries", nr_to_scan);
162 spin_lock(&mb_cache_spinlock);
163 while (nr_to_scan-- && !list_empty(&mb_cache_lru_list)) {
164 struct mb_cache_entry *ce =
165 list_entry(mb_cache_lru_list.next,
166 struct mb_cache_entry, e_lru_list);
167 list_move_tail(&ce->e_lru_list, &free_list);
168 __mb_cache_entry_unhash(ce);
169 freed++;
170 }
171 spin_unlock(&mb_cache_spinlock);
172 list_for_each_entry_safe(entry, tmp, &free_list, e_lru_list) {
173 __mb_cache_entry_forget(entry, gfp_mask);
174 }
175 return freed;
176}
177
178static unsigned long
179mb_cache_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
180{
181 struct mb_cache *cache;
182 unsigned long count = 0;
183
184 spin_lock(&mb_cache_spinlock);
185 list_for_each_entry(cache, &mb_cache_list, c_cache_list) {
186 mb_debug("cache %s (%d)", cache->c_name,
187 atomic_read(&cache->c_entry_count));
188 count += atomic_read(&cache->c_entry_count);
189 }
190 spin_unlock(&mb_cache_spinlock);
191
192 return vfs_pressure_ratio(count);
193}
194
195static struct shrinker mb_cache_shrinker = {
196 .count_objects = mb_cache_shrink_count,
197 .scan_objects = mb_cache_shrink_scan,
198 .seeks = DEFAULT_SEEKS,
199};
200
201/*
202 * mb_cache_create() create a new cache
203 *
204 * All entries in one cache are equal size. Cache entries may be from
205 * multiple devices. If this is the first mbcache created, registers
206 * the cache with kernel memory management. Returns NULL if no more
207 * memory was available.
208 *
209 * @name: name of the cache (informal)
210 * @bucket_bits: log2(number of hash buckets)
211 */
212struct mb_cache *
213mb_cache_create(const char *name, int bucket_bits)
214{
215 int n, bucket_count = 1 << bucket_bits;
216 struct mb_cache *cache = NULL;
217
218 cache = kmalloc(sizeof(struct mb_cache), GFP_KERNEL);
219 if (!cache)
220 return NULL;
221 cache->c_name = name;
222 atomic_set(&cache->c_entry_count, 0);
223 cache->c_bucket_bits = bucket_bits;
224 cache->c_block_hash = kmalloc(bucket_count * sizeof(struct list_head),
225 GFP_KERNEL);
226 if (!cache->c_block_hash)
227 goto fail;
228 for (n=0; n<bucket_count; n++)
229 INIT_LIST_HEAD(&cache->c_block_hash[n]);
230 cache->c_index_hash = kmalloc(bucket_count * sizeof(struct list_head),
231 GFP_KERNEL);
232 if (!cache->c_index_hash)
233 goto fail;
234 for (n=0; n<bucket_count; n++)
235 INIT_LIST_HEAD(&cache->c_index_hash[n]);
236 cache->c_entry_cache = kmem_cache_create(name,
237 sizeof(struct mb_cache_entry), 0,
238 SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL);
239 if (!cache->c_entry_cache)
240 goto fail2;
241
242 /*
243 * Set an upper limit on the number of cache entries so that the hash
244 * chains won't grow too long.
245 */
246 cache->c_max_entries = bucket_count << 4;
247
248 spin_lock(&mb_cache_spinlock);
249 list_add(&cache->c_cache_list, &mb_cache_list);
250 spin_unlock(&mb_cache_spinlock);
251 return cache;
252
253fail2:
254 kfree(cache->c_index_hash);
255
256fail:
257 kfree(cache->c_block_hash);
258 kfree(cache);
259 return NULL;
260}
261
262
263/*
264 * mb_cache_shrink()
265 *
266 * Removes all cache entries of a device from the cache. All cache entries
267 * currently in use cannot be freed, and thus remain in the cache. All others
268 * are freed.
269 *
270 * @bdev: which device's cache entries to shrink
271 */
272void
273mb_cache_shrink(struct block_device *bdev)
274{
275 LIST_HEAD(free_list);
276 struct list_head *l, *ltmp;
277
278 spin_lock(&mb_cache_spinlock);
279 list_for_each_safe(l, ltmp, &mb_cache_lru_list) {
280 struct mb_cache_entry *ce =
281 list_entry(l, struct mb_cache_entry, e_lru_list);
282 if (ce->e_bdev == bdev) {
283 list_move_tail(&ce->e_lru_list, &free_list);
284 __mb_cache_entry_unhash(ce);
285 }
286 }
287 spin_unlock(&mb_cache_spinlock);
288 list_for_each_safe(l, ltmp, &free_list) {
289 __mb_cache_entry_forget(list_entry(l, struct mb_cache_entry,
290 e_lru_list), GFP_KERNEL);
291 }
292}
293
294
295/*
296 * mb_cache_destroy()
297 *
298 * Shrinks the cache to its minimum possible size (hopefully 0 entries),
299 * and then destroys it. If this was the last mbcache, un-registers the
300 * mbcache from kernel memory management.
301 */
302void
303mb_cache_destroy(struct mb_cache *cache)
304{
305 LIST_HEAD(free_list);
306 struct list_head *l, *ltmp;
307
308 spin_lock(&mb_cache_spinlock);
309 list_for_each_safe(l, ltmp, &mb_cache_lru_list) {
310 struct mb_cache_entry *ce =
311 list_entry(l, struct mb_cache_entry, e_lru_list);
312 if (ce->e_cache == cache) {
313 list_move_tail(&ce->e_lru_list, &free_list);
314 __mb_cache_entry_unhash(ce);
315 }
316 }
317 list_del(&cache->c_cache_list);
318 spin_unlock(&mb_cache_spinlock);
319
320 list_for_each_safe(l, ltmp, &free_list) {
321 __mb_cache_entry_forget(list_entry(l, struct mb_cache_entry,
322 e_lru_list), GFP_KERNEL);
323 }
324
325 if (atomic_read(&cache->c_entry_count) > 0) {
326 mb_error("cache %s: %d orphaned entries",
327 cache->c_name,
328 atomic_read(&cache->c_entry_count));
329 }
330
331 kmem_cache_destroy(cache->c_entry_cache);
332
333 kfree(cache->c_index_hash);
334 kfree(cache->c_block_hash);
335 kfree(cache);
336}
337
338/*
339 * mb_cache_entry_alloc()
340 *
341 * Allocates a new cache entry. The new entry will not be valid initially,
342 * and thus cannot be looked up yet. It should be filled with data, and
343 * then inserted into the cache using mb_cache_entry_insert(). Returns NULL
344 * if no more memory was available.
345 */
346struct mb_cache_entry *
347mb_cache_entry_alloc(struct mb_cache *cache, gfp_t gfp_flags)
348{
349 struct mb_cache_entry *ce = NULL;
350
351 if (atomic_read(&cache->c_entry_count) >= cache->c_max_entries) {
352 spin_lock(&mb_cache_spinlock);
353 if (!list_empty(&mb_cache_lru_list)) {
354 ce = list_entry(mb_cache_lru_list.next,
355 struct mb_cache_entry, e_lru_list);
356 list_del_init(&ce->e_lru_list);
357 __mb_cache_entry_unhash(ce);
358 }
359 spin_unlock(&mb_cache_spinlock);
360 }
361 if (!ce) {
362 ce = kmem_cache_alloc(cache->c_entry_cache, gfp_flags);
363 if (!ce)
364 return NULL;
365 atomic_inc(&cache->c_entry_count);
366 INIT_LIST_HEAD(&ce->e_lru_list);
367 INIT_LIST_HEAD(&ce->e_block_list);
368 ce->e_cache = cache;
369 ce->e_queued = 0;
370 }
371 ce->e_used = 1 + MB_CACHE_WRITER;
372 return ce;
373}
374
375
376/*
377 * mb_cache_entry_insert()
378 *
379 * Inserts an entry that was allocated using mb_cache_entry_alloc() into
380 * the cache. After this, the cache entry can be looked up, but is not yet
381 * in the lru list as the caller still holds a handle to it. Returns 0 on
382 * success, or -EBUSY if a cache entry for that device + inode exists
383 * already (this may happen after a failed lookup, but when another process
384 * has inserted the same cache entry in the meantime).
385 *
386 * @bdev: device the cache entry belongs to
387 * @block: block number
388 * @key: lookup key
389 */
390int
391mb_cache_entry_insert(struct mb_cache_entry *ce, struct block_device *bdev,
392 sector_t block, unsigned int key)
393{
394 struct mb_cache *cache = ce->e_cache;
395 unsigned int bucket;
396 struct list_head *l;
397 int error = -EBUSY;
398
399 bucket = hash_long((unsigned long)bdev + (block & 0xffffffff),
400 cache->c_bucket_bits);
401 spin_lock(&mb_cache_spinlock);
402 list_for_each_prev(l, &cache->c_block_hash[bucket]) {
403 struct mb_cache_entry *ce =
404 list_entry(l, struct mb_cache_entry, e_block_list);
405 if (ce->e_bdev == bdev && ce->e_block == block)
406 goto out;
407 }
408 __mb_cache_entry_unhash(ce);
409 ce->e_bdev = bdev;
410 ce->e_block = block;
411 list_add(&ce->e_block_list, &cache->c_block_hash[bucket]);
412 ce->e_index.o_key = key;
413 bucket = hash_long(key, cache->c_bucket_bits);
414 list_add(&ce->e_index.o_list, &cache->c_index_hash[bucket]);
415 error = 0;
416out:
417 spin_unlock(&mb_cache_spinlock);
418 return error;
419}
420
421
422/*
423 * mb_cache_entry_release()
424 *
425 * Release a handle to a cache entry. When the last handle to a cache entry
426 * is released it is either freed (if it is invalid) or otherwise inserted
427 * in to the lru list.
428 */
429void
430mb_cache_entry_release(struct mb_cache_entry *ce)
431{
432 spin_lock(&mb_cache_spinlock);
433 __mb_cache_entry_release_unlock(ce);
434}
435
436
437/*
438 * mb_cache_entry_free()
439 *
440 * This is equivalent to the sequence mb_cache_entry_takeout() --
441 * mb_cache_entry_release().
442 */
443void
444mb_cache_entry_free(struct mb_cache_entry *ce)
445{
446 spin_lock(&mb_cache_spinlock);
447 mb_assert(list_empty(&ce->e_lru_list));
448 __mb_cache_entry_unhash(ce);
449 __mb_cache_entry_release_unlock(ce);
450}
451
452
453/*
454 * mb_cache_entry_get()
455 *
456 * Get a cache entry by device / block number. (There can only be one entry
457 * in the cache per device and block.) Returns NULL if no such cache entry
458 * exists. The returned cache entry is locked for exclusive access ("single
459 * writer").
460 */
461struct mb_cache_entry *
462mb_cache_entry_get(struct mb_cache *cache, struct block_device *bdev,
463 sector_t block)
464{
465 unsigned int bucket;
466 struct list_head *l;
467 struct mb_cache_entry *ce;
468
469 bucket = hash_long((unsigned long)bdev + (block & 0xffffffff),
470 cache->c_bucket_bits);
471 spin_lock(&mb_cache_spinlock);
472 list_for_each(l, &cache->c_block_hash[bucket]) {
473 ce = list_entry(l, struct mb_cache_entry, e_block_list);
474 if (ce->e_bdev == bdev && ce->e_block == block) {
475 DEFINE_WAIT(wait);
476
477 if (!list_empty(&ce->e_lru_list))
478 list_del_init(&ce->e_lru_list);
479
480 while (ce->e_used > 0) {
481 ce->e_queued++;
482 prepare_to_wait(&mb_cache_queue, &wait,
483 TASK_UNINTERRUPTIBLE);
484 spin_unlock(&mb_cache_spinlock);
485 schedule();
486 spin_lock(&mb_cache_spinlock);
487 ce->e_queued--;
488 }
489 finish_wait(&mb_cache_queue, &wait);
490 ce->e_used += 1 + MB_CACHE_WRITER;
491
492 if (!__mb_cache_entry_is_hashed(ce)) {
493 __mb_cache_entry_release_unlock(ce);
494 return NULL;
495 }
496 goto cleanup;
497 }
498 }
499 ce = NULL;
500
501cleanup:
502 spin_unlock(&mb_cache_spinlock);
503 return ce;
504}
505
506#if !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0)
507
508static struct mb_cache_entry *
509__mb_cache_entry_find(struct list_head *l, struct list_head *head,
510 struct block_device *bdev, unsigned int key)
511{
512 while (l != head) {
513 struct mb_cache_entry *ce =
514 list_entry(l, struct mb_cache_entry, e_index.o_list);
515 if (ce->e_bdev == bdev && ce->e_index.o_key == key) {
516 DEFINE_WAIT(wait);
517
518 if (!list_empty(&ce->e_lru_list))
519 list_del_init(&ce->e_lru_list);
520
521 /* Incrementing before holding the lock gives readers
522 priority over writers. */
523 ce->e_used++;
524 while (ce->e_used >= MB_CACHE_WRITER) {
525 ce->e_queued++;
526 prepare_to_wait(&mb_cache_queue, &wait,
527 TASK_UNINTERRUPTIBLE);
528 spin_unlock(&mb_cache_spinlock);
529 schedule();
530 spin_lock(&mb_cache_spinlock);
531 ce->e_queued--;
532 }
533 finish_wait(&mb_cache_queue, &wait);
534
535 if (!__mb_cache_entry_is_hashed(ce)) {
536 __mb_cache_entry_release_unlock(ce);
537 spin_lock(&mb_cache_spinlock);
538 return ERR_PTR(-EAGAIN);
539 }
540 return ce;
541 }
542 l = l->next;
543 }
544 return NULL;
545}
546
547
548/*
549 * mb_cache_entry_find_first()
550 *
551 * Find the first cache entry on a given device with a certain key in
552 * an additional index. Additional matches can be found with
553 * mb_cache_entry_find_next(). Returns NULL if no match was found. The
554 * returned cache entry is locked for shared access ("multiple readers").
555 *
556 * @cache: the cache to search
557 * @bdev: the device the cache entry should belong to
558 * @key: the key in the index
559 */
560struct mb_cache_entry *
561mb_cache_entry_find_first(struct mb_cache *cache, struct block_device *bdev,
562 unsigned int key)
563{
564 unsigned int bucket = hash_long(key, cache->c_bucket_bits);
565 struct list_head *l;
566 struct mb_cache_entry *ce;
567
568 spin_lock(&mb_cache_spinlock);
569 l = cache->c_index_hash[bucket].next;
570 ce = __mb_cache_entry_find(l, &cache->c_index_hash[bucket], bdev, key);
571 spin_unlock(&mb_cache_spinlock);
572 return ce;
573}
574
575
576/*
577 * mb_cache_entry_find_next()
578 *
579 * Find the next cache entry on a given device with a certain key in an
580 * additional index. Returns NULL if no match could be found. The previous
581 * entry is atomatically released, so that mb_cache_entry_find_next() can
582 * be called like this:
583 *
584 * entry = mb_cache_entry_find_first();
585 * while (entry) {
586 * ...
587 * entry = mb_cache_entry_find_next(entry, ...);
588 * }
589 *
590 * @prev: The previous match
591 * @bdev: the device the cache entry should belong to
592 * @key: the key in the index
593 */
594struct mb_cache_entry *
595mb_cache_entry_find_next(struct mb_cache_entry *prev,
596 struct block_device *bdev, unsigned int key)
597{
598 struct mb_cache *cache = prev->e_cache;
599 unsigned int bucket = hash_long(key, cache->c_bucket_bits);
600 struct list_head *l;
601 struct mb_cache_entry *ce;
602
603 spin_lock(&mb_cache_spinlock);
604 l = prev->e_index.o_list.next;
605 ce = __mb_cache_entry_find(l, &cache->c_index_hash[bucket], bdev, key);
606 __mb_cache_entry_release_unlock(prev);
607 return ce;
608}
609
610#endif /* !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0) */
611
612static int __init init_mbcache(void)
613{
614 register_shrinker(&mb_cache_shrinker);
615 return 0;
616}
617
618static void __exit exit_mbcache(void)
619{
620 unregister_shrinker(&mb_cache_shrinker);
621}
622
623module_init(init_mbcache)
624module_exit(exit_mbcache)
625