mbcache.c 11.7 KB
Newer Older
Jan Kara's avatar
Jan Kara committed
1 2 3 4 5 6
#include <linux/spinlock.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/list_bl.h>
#include <linux/module.h>
#include <linux/sched.h>
Jan Kara's avatar
Jan Kara committed
7
#include <linux/workqueue.h>
Jan Kara's avatar
Jan Kara committed
8
#include <linux/mbcache.h>
Jan Kara's avatar
Jan Kara committed
9 10 11 12

/*
 * Mbcache is a simple key-value store. Keys need not be unique, however
 * key-value pairs are expected to be unique (we use this fact in
13
 * mb_cache_entry_delete()).
Jan Kara's avatar
Jan Kara committed
14 15 16 17 18 19 20 21 22 23 24 25
 *
 * Ext2 and ext4 use this cache for deduplication of extended attribute blocks.
 * They use hash of a block contents as a key and block number as a value.
 * That's why keys need not be unique (different xattr blocks may end up having
 * the same hash). However block number always uniquely identifies a cache
 * entry.
 *
 * We provide functions for creation and removal of entries, search by key,
 * and a special "delete entry with given key-value pair" operation. Fixed
 * size hash table is used for fast key lookups.
 */

Jan Kara's avatar
Jan Kara committed
26
struct mb_cache {
Jan Kara's avatar
Jan Kara committed
27 28 29 30
	/* Hash table of entries */
	struct hlist_bl_head	*c_hash;
	/* log2 of hash table size */
	int			c_bucket_bits;
Jan Kara's avatar
Jan Kara committed
31
	/* Maximum entries in cache to avoid degrading hash too much */
32
	unsigned long		c_max_entries;
33 34 35
	/* Protects c_list, c_entry_count */
	spinlock_t		c_list_lock;
	struct list_head	c_list;
Jan Kara's avatar
Jan Kara committed
36 37 38
	/* Number of entries in cache */
	unsigned long		c_entry_count;
	struct shrinker		c_shrink;
Jan Kara's avatar
Jan Kara committed
39 40
	/* Work for shrinking when the cache has too many entries */
	struct work_struct	c_shrink_work;
Jan Kara's avatar
Jan Kara committed
41 42
};

Jan Kara's avatar
Jan Kara committed
43
static struct kmem_cache *mb_entry_cache;
Jan Kara's avatar
Jan Kara committed
44

Jan Kara's avatar
Jan Kara committed
45
static unsigned long mb_cache_shrink(struct mb_cache *cache,
46
				     unsigned long nr_to_scan);
Jan Kara's avatar
Jan Kara committed
47

48 49
static inline struct hlist_bl_head *mb_cache_entry_head(struct mb_cache *cache,
							u32 key)
50
{
51
	return &cache->c_hash[hash_32(key, cache->c_bucket_bits)];
52 53
}

Jan Kara's avatar
Jan Kara committed
54 55 56 57 58 59
/*
 * Number of entries to reclaim synchronously when there are too many entries
 * in cache
 */
#define SYNC_SHRINK_BATCH 64

Jan Kara's avatar
Jan Kara committed
60
/*
Jan Kara's avatar
Jan Kara committed
61
 * mb_cache_entry_create - create entry in cache
Jan Kara's avatar
Jan Kara committed
62 63 64
 * @cache - cache where the entry should be created
 * @mask - gfp mask with which the entry should be allocated
 * @key - key of the entry
65 66
 * @value - value of the entry
 * @reusable - is the entry reusable by others?
Jan Kara's avatar
Jan Kara committed
67
 *
68 69 70
 * Creates entry in @cache with key @key and value @value. The function returns
 * -EBUSY if entry with the same key and value already exists in cache.
 * Otherwise 0 is returned.
Jan Kara's avatar
Jan Kara committed
71
 */
Jan Kara's avatar
Jan Kara committed
72
int mb_cache_entry_create(struct mb_cache *cache, gfp_t mask, u32 key,
73
			  u64 value, bool reusable)
Jan Kara's avatar
Jan Kara committed
74
{
Jan Kara's avatar
Jan Kara committed
75
	struct mb_cache_entry *entry, *dup;
Jan Kara's avatar
Jan Kara committed
76 77 78
	struct hlist_bl_node *dup_node;
	struct hlist_bl_head *head;

Jan Kara's avatar
Jan Kara committed
79 80 81 82 83
	/* Schedule background reclaim if there are too many entries */
	if (cache->c_entry_count >= cache->c_max_entries)
		schedule_work(&cache->c_shrink_work);
	/* Do some sync reclaim if background reclaim cannot keep up */
	if (cache->c_entry_count >= 2*cache->c_max_entries)
Jan Kara's avatar
Jan Kara committed
84
		mb_cache_shrink(cache, SYNC_SHRINK_BATCH);
Jan Kara's avatar
Jan Kara committed
85

Jan Kara's avatar
Jan Kara committed
86
	entry = kmem_cache_alloc(mb_entry_cache, mask);
Jan Kara's avatar
Jan Kara committed
87 88 89
	if (!entry)
		return -ENOMEM;

90
	INIT_LIST_HEAD(&entry->e_list);
Jan Kara's avatar
Jan Kara committed
91 92 93
	/* One ref for hash, one ref returned */
	atomic_set(&entry->e_refcnt, 1);
	entry->e_key = key;
94
	entry->e_value = value;
95
	entry->e_reusable = reusable;
96
	head = mb_cache_entry_head(cache, key);
Jan Kara's avatar
Jan Kara committed
97 98
	hlist_bl_lock(head);
	hlist_bl_for_each_entry(dup, dup_node, head, e_hash_list) {
99
		if (dup->e_key == key && dup->e_value == value) {
Jan Kara's avatar
Jan Kara committed
100
			hlist_bl_unlock(head);
Jan Kara's avatar
Jan Kara committed
101
			kmem_cache_free(mb_entry_cache, entry);
Jan Kara's avatar
Jan Kara committed
102 103 104 105 106 107
			return -EBUSY;
		}
	}
	hlist_bl_add_head(&entry->e_hash_list, head);
	hlist_bl_unlock(head);

108 109
	spin_lock(&cache->c_list_lock);
	list_add_tail(&entry->e_list, &cache->c_list);
Jan Kara's avatar
Jan Kara committed
110 111 112
	/* Grab ref for LRU list */
	atomic_inc(&entry->e_refcnt);
	cache->c_entry_count++;
113
	spin_unlock(&cache->c_list_lock);
Jan Kara's avatar
Jan Kara committed
114 115 116

	return 0;
}
Jan Kara's avatar
Jan Kara committed
117
EXPORT_SYMBOL(mb_cache_entry_create);
Jan Kara's avatar
Jan Kara committed
118

Jan Kara's avatar
Jan Kara committed
119
void __mb_cache_entry_free(struct mb_cache_entry *entry)
Jan Kara's avatar
Jan Kara committed
120
{
Jan Kara's avatar
Jan Kara committed
121
	kmem_cache_free(mb_entry_cache, entry);
Jan Kara's avatar
Jan Kara committed
122
}
Jan Kara's avatar
Jan Kara committed
123
EXPORT_SYMBOL(__mb_cache_entry_free);
Jan Kara's avatar
Jan Kara committed
124

Jan Kara's avatar
Jan Kara committed
125 126 127
static struct mb_cache_entry *__entry_find(struct mb_cache *cache,
					   struct mb_cache_entry *entry,
					   u32 key)
Jan Kara's avatar
Jan Kara committed
128
{
Jan Kara's avatar
Jan Kara committed
129
	struct mb_cache_entry *old_entry = entry;
Jan Kara's avatar
Jan Kara committed
130 131 132
	struct hlist_bl_node *node;
	struct hlist_bl_head *head;

133
	head = mb_cache_entry_head(cache, key);
Jan Kara's avatar
Jan Kara committed
134 135 136 137 138 139
	hlist_bl_lock(head);
	if (entry && !hlist_bl_unhashed(&entry->e_hash_list))
		node = entry->e_hash_list.next;
	else
		node = hlist_bl_first(head);
	while (node) {
Jan Kara's avatar
Jan Kara committed
140
		entry = hlist_bl_entry(node, struct mb_cache_entry,
Jan Kara's avatar
Jan Kara committed
141
				       e_hash_list);
142
		if (entry->e_key == key && entry->e_reusable) {
Jan Kara's avatar
Jan Kara committed
143 144 145 146 147 148 149 150 151
			atomic_inc(&entry->e_refcnt);
			goto out;
		}
		node = node->next;
	}
	entry = NULL;
out:
	hlist_bl_unlock(head);
	if (old_entry)
Jan Kara's avatar
Jan Kara committed
152
		mb_cache_entry_put(cache, old_entry);
Jan Kara's avatar
Jan Kara committed
153 154 155 156 157

	return entry;
}

/*
158
 * mb_cache_entry_find_first - find the first reusable entry with the given key
Jan Kara's avatar
Jan Kara committed
159 160 161
 * @cache: cache where we should search
 * @key: key to look for
 *
162 163
 * Search in @cache for a reusable entry with key @key. Grabs reference to the
 * first reusable entry found and returns the entry.
Jan Kara's avatar
Jan Kara committed
164
 */
Jan Kara's avatar
Jan Kara committed
165 166
struct mb_cache_entry *mb_cache_entry_find_first(struct mb_cache *cache,
						 u32 key)
Jan Kara's avatar
Jan Kara committed
167 168 169
{
	return __entry_find(cache, NULL, key);
}
Jan Kara's avatar
Jan Kara committed
170
EXPORT_SYMBOL(mb_cache_entry_find_first);
Jan Kara's avatar
Jan Kara committed
171 172

/*
173
 * mb_cache_entry_find_next - find next reusable entry with the same key
Jan Kara's avatar
Jan Kara committed
174 175 176
 * @cache: cache where we should search
 * @entry: entry to start search from
 *
177 178 179 180
 * Finds next reusable entry in the hash chain which has the same key as @entry.
 * If @entry is unhashed (which can happen when deletion of entry races with the
 * search), finds the first reusable entry in the hash chain. The function drops
 * reference to @entry and returns with a reference to the found entry.
Jan Kara's avatar
Jan Kara committed
181
 */
Jan Kara's avatar
Jan Kara committed
182 183
struct mb_cache_entry *mb_cache_entry_find_next(struct mb_cache *cache,
						struct mb_cache_entry *entry)
Jan Kara's avatar
Jan Kara committed
184 185 186
{
	return __entry_find(cache, entry, entry->e_key);
}
Jan Kara's avatar
Jan Kara committed
187
EXPORT_SYMBOL(mb_cache_entry_find_next);
Jan Kara's avatar
Jan Kara committed
188

189
/*
190
 * mb_cache_entry_get - get a cache entry by value (and key)
191
 * @cache - cache we work with
192 193
 * @key - key
 * @value - value
194 195
 */
struct mb_cache_entry *mb_cache_entry_get(struct mb_cache *cache, u32 key,
196
					  u64 value)
197 198 199 200 201 202 203 204
{
	struct hlist_bl_node *node;
	struct hlist_bl_head *head;
	struct mb_cache_entry *entry;

	head = mb_cache_entry_head(cache, key);
	hlist_bl_lock(head);
	hlist_bl_for_each_entry(entry, node, head, e_hash_list) {
205
		if (entry->e_key == key && entry->e_value == value) {
206 207 208 209 210 211 212 213 214 215 216
			atomic_inc(&entry->e_refcnt);
			goto out;
		}
	}
	entry = NULL;
out:
	hlist_bl_unlock(head);
	return entry;
}
EXPORT_SYMBOL(mb_cache_entry_get);

217
/* mb_cache_entry_delete - remove a cache entry
Jan Kara's avatar
Jan Kara committed
218
 * @cache - cache we work with
219 220
 * @key - key
 * @value - value
Jan Kara's avatar
Jan Kara committed
221
 *
222
 * Remove entry from cache @cache with key @key and value @value.
Jan Kara's avatar
Jan Kara committed
223
 */
224
void mb_cache_entry_delete(struct mb_cache *cache, u32 key, u64 value)
Jan Kara's avatar
Jan Kara committed
225 226 227
{
	struct hlist_bl_node *node;
	struct hlist_bl_head *head;
Jan Kara's avatar
Jan Kara committed
228
	struct mb_cache_entry *entry;
Jan Kara's avatar
Jan Kara committed
229

230
	head = mb_cache_entry_head(cache, key);
Jan Kara's avatar
Jan Kara committed
231 232
	hlist_bl_lock(head);
	hlist_bl_for_each_entry(entry, node, head, e_hash_list) {
233
		if (entry->e_key == key && entry->e_value == value) {
Jan Kara's avatar
Jan Kara committed
234 235 236
			/* We keep hash list reference to keep entry alive */
			hlist_bl_del_init(&entry->e_hash_list);
			hlist_bl_unlock(head);
237 238 239
			spin_lock(&cache->c_list_lock);
			if (!list_empty(&entry->e_list)) {
				list_del_init(&entry->e_list);
Jan Kara's avatar
Jan Kara committed
240 241 242
				cache->c_entry_count--;
				atomic_dec(&entry->e_refcnt);
			}
243
			spin_unlock(&cache->c_list_lock);
Jan Kara's avatar
Jan Kara committed
244
			mb_cache_entry_put(cache, entry);
Jan Kara's avatar
Jan Kara committed
245 246 247 248 249
			return;
		}
	}
	hlist_bl_unlock(head);
}
250
EXPORT_SYMBOL(mb_cache_entry_delete);
Jan Kara's avatar
Jan Kara committed
251

Jan Kara's avatar
Jan Kara committed
252
/* mb_cache_entry_touch - cache entry got used
Jan Kara's avatar
Jan Kara committed
253 254 255
 * @cache - cache the entry belongs to
 * @entry - entry that got used
 *
256
 * Marks entry as used to give hit higher chances of surviving in cache.
Jan Kara's avatar
Jan Kara committed
257
 */
Jan Kara's avatar
Jan Kara committed
258 259
void mb_cache_entry_touch(struct mb_cache *cache,
			  struct mb_cache_entry *entry)
Jan Kara's avatar
Jan Kara committed
260
{
261
	entry->e_referenced = 1;
Jan Kara's avatar
Jan Kara committed
262
}
Jan Kara's avatar
Jan Kara committed
263
EXPORT_SYMBOL(mb_cache_entry_touch);
Jan Kara's avatar
Jan Kara committed
264

Jan Kara's avatar
Jan Kara committed
265 266
static unsigned long mb_cache_count(struct shrinker *shrink,
				    struct shrink_control *sc)
Jan Kara's avatar
Jan Kara committed
267
{
Jan Kara's avatar
Jan Kara committed
268 269
	struct mb_cache *cache = container_of(shrink, struct mb_cache,
					      c_shrink);
Jan Kara's avatar
Jan Kara committed
270 271 272 273 274

	return cache->c_entry_count;
}

/* Shrink number of entries in cache */
Jan Kara's avatar
Jan Kara committed
275
static unsigned long mb_cache_shrink(struct mb_cache *cache,
276
				     unsigned long nr_to_scan)
Jan Kara's avatar
Jan Kara committed
277
{
Jan Kara's avatar
Jan Kara committed
278
	struct mb_cache_entry *entry;
Jan Kara's avatar
Jan Kara committed
279
	struct hlist_bl_head *head;
280
	unsigned long shrunk = 0;
Jan Kara's avatar
Jan Kara committed
281

282 283 284
	spin_lock(&cache->c_list_lock);
	while (nr_to_scan-- && !list_empty(&cache->c_list)) {
		entry = list_first_entry(&cache->c_list,
Jan Kara's avatar
Jan Kara committed
285
					 struct mb_cache_entry, e_list);
286 287
		if (entry->e_referenced) {
			entry->e_referenced = 0;
288
			list_move_tail(&entry->e_list, &cache->c_list);
289 290 291
			continue;
		}
		list_del_init(&entry->e_list);
Jan Kara's avatar
Jan Kara committed
292 293 294 295 296
		cache->c_entry_count--;
		/*
		 * We keep LRU list reference so that entry doesn't go away
		 * from under us.
		 */
297
		spin_unlock(&cache->c_list_lock);
298
		head = mb_cache_entry_head(cache, entry->e_key);
Jan Kara's avatar
Jan Kara committed
299 300 301 302 303 304
		hlist_bl_lock(head);
		if (!hlist_bl_unhashed(&entry->e_hash_list)) {
			hlist_bl_del_init(&entry->e_hash_list);
			atomic_dec(&entry->e_refcnt);
		}
		hlist_bl_unlock(head);
Jan Kara's avatar
Jan Kara committed
305
		if (mb_cache_entry_put(cache, entry))
Jan Kara's avatar
Jan Kara committed
306 307
			shrunk++;
		cond_resched();
308
		spin_lock(&cache->c_list_lock);
Jan Kara's avatar
Jan Kara committed
309
	}
310
	spin_unlock(&cache->c_list_lock);
Jan Kara's avatar
Jan Kara committed
311 312 313 314

	return shrunk;
}

Jan Kara's avatar
Jan Kara committed
315 316
static unsigned long mb_cache_scan(struct shrinker *shrink,
				   struct shrink_control *sc)
Jan Kara's avatar
Jan Kara committed
317
{
Jan Kara's avatar
Jan Kara committed
318
	struct mb_cache *cache = container_of(shrink, struct mb_cache,
Jan Kara's avatar
Jan Kara committed
319
					      c_shrink);
320
	return mb_cache_shrink(cache, sc->nr_to_scan);
Jan Kara's avatar
Jan Kara committed
321 322 323 324 325
}

/* We shrink 1/X of the cache when we have too many entries in it */
#define SHRINK_DIVISOR 16

Jan Kara's avatar
Jan Kara committed
326
static void mb_cache_shrink_worker(struct work_struct *work)
Jan Kara's avatar
Jan Kara committed
327
{
Jan Kara's avatar
Jan Kara committed
328 329 330
	struct mb_cache *cache = container_of(work, struct mb_cache,
					      c_shrink_work);
	mb_cache_shrink(cache, cache->c_max_entries / SHRINK_DIVISOR);
Jan Kara's avatar
Jan Kara committed
331 332
}

Jan Kara's avatar
Jan Kara committed
333
/*
Jan Kara's avatar
Jan Kara committed
334
 * mb_cache_create - create cache
Jan Kara's avatar
Jan Kara committed
335 336 337 338
 * @bucket_bits: log2 of the hash table size
 *
 * Create cache for keys with 2^bucket_bits hash entries.
 */
Jan Kara's avatar
Jan Kara committed
339
struct mb_cache *mb_cache_create(int bucket_bits)
Jan Kara's avatar
Jan Kara committed
340
{
Jan Kara's avatar
Jan Kara committed
341
	struct mb_cache *cache;
342 343
	unsigned long bucket_count = 1UL << bucket_bits;
	unsigned long i;
Jan Kara's avatar
Jan Kara committed
344

Jan Kara's avatar
Jan Kara committed
345
	cache = kzalloc(sizeof(struct mb_cache), GFP_KERNEL);
Jan Kara's avatar
Jan Kara committed
346 347 348
	if (!cache)
		goto err_out;
	cache->c_bucket_bits = bucket_bits;
Jan Kara's avatar
Jan Kara committed
349
	cache->c_max_entries = bucket_count << 4;
350 351
	INIT_LIST_HEAD(&cache->c_list);
	spin_lock_init(&cache->c_list_lock);
Jan Kara's avatar
Jan Kara committed
352 353 354 355 356 357 358 359 360
	cache->c_hash = kmalloc(bucket_count * sizeof(struct hlist_bl_head),
				GFP_KERNEL);
	if (!cache->c_hash) {
		kfree(cache);
		goto err_out;
	}
	for (i = 0; i < bucket_count; i++)
		INIT_HLIST_BL_HEAD(&cache->c_hash[i]);

Jan Kara's avatar
Jan Kara committed
361 362
	cache->c_shrink.count_objects = mb_cache_count;
	cache->c_shrink.scan_objects = mb_cache_scan;
Jan Kara's avatar
Jan Kara committed
363
	cache->c_shrink.seeks = DEFAULT_SEEKS;
364 365 366 367 368
	if (register_shrinker(&cache->c_shrink)) {
		kfree(cache->c_hash);
		kfree(cache);
		goto err_out;
	}
Jan Kara's avatar
Jan Kara committed
369

Jan Kara's avatar
Jan Kara committed
370
	INIT_WORK(&cache->c_shrink_work, mb_cache_shrink_worker);
Jan Kara's avatar
Jan Kara committed
371

Jan Kara's avatar
Jan Kara committed
372 373 374 375 376
	return cache;

err_out:
	return NULL;
}
Jan Kara's avatar
Jan Kara committed
377
EXPORT_SYMBOL(mb_cache_create);
Jan Kara's avatar
Jan Kara committed
378 379

/*
Jan Kara's avatar
Jan Kara committed
380
 * mb_cache_destroy - destroy cache
Jan Kara's avatar
Jan Kara committed
381 382 383 384 385
 * @cache: the cache to destroy
 *
 * Free all entries in cache and cache itself. Caller must make sure nobody
 * (except shrinker) can reach @cache when calling this.
 */
Jan Kara's avatar
Jan Kara committed
386
void mb_cache_destroy(struct mb_cache *cache)
Jan Kara's avatar
Jan Kara committed
387
{
Jan Kara's avatar
Jan Kara committed
388
	struct mb_cache_entry *entry, *next;
Jan Kara's avatar
Jan Kara committed
389 390 391 392 393 394 395

	unregister_shrinker(&cache->c_shrink);

	/*
	 * We don't bother with any locking. Cache must not be used at this
	 * point.
	 */
396
	list_for_each_entry_safe(entry, next, &cache->c_list, e_list) {
Jan Kara's avatar
Jan Kara committed
397 398 399 400 401
		if (!hlist_bl_unhashed(&entry->e_hash_list)) {
			hlist_bl_del_init(&entry->e_hash_list);
			atomic_dec(&entry->e_refcnt);
		} else
			WARN_ON(1);
402
		list_del(&entry->e_list);
Jan Kara's avatar
Jan Kara committed
403
		WARN_ON(atomic_read(&entry->e_refcnt) != 1);
Jan Kara's avatar
Jan Kara committed
404
		mb_cache_entry_put(cache, entry);
Jan Kara's avatar
Jan Kara committed
405 406 407 408
	}
	kfree(cache->c_hash);
	kfree(cache);
}
Jan Kara's avatar
Jan Kara committed
409
EXPORT_SYMBOL(mb_cache_destroy);
Jan Kara's avatar
Jan Kara committed
410

Jan Kara's avatar
Jan Kara committed
411
static int __init mbcache_init(void)
Jan Kara's avatar
Jan Kara committed
412
{
Jan Kara's avatar
Jan Kara committed
413 414
	mb_entry_cache = kmem_cache_create("mbcache",
				sizeof(struct mb_cache_entry), 0,
Jan Kara's avatar
Jan Kara committed
415
				SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL);
416 417
	if (!mb_entry_cache)
		return -ENOMEM;
Jan Kara's avatar
Jan Kara committed
418 419 420
	return 0;
}

Jan Kara's avatar
Jan Kara committed
421
static void __exit mbcache_exit(void)
Jan Kara's avatar
Jan Kara committed
422
{
Jan Kara's avatar
Jan Kara committed
423
	kmem_cache_destroy(mb_entry_cache);
Jan Kara's avatar
Jan Kara committed
424 425
}

Jan Kara's avatar
Jan Kara committed
426 427
module_init(mbcache_init)
module_exit(mbcache_exit)
Jan Kara's avatar
Jan Kara committed
428 429 430 431

MODULE_AUTHOR("Jan Kara <jack@suse.cz>");
MODULE_DESCRIPTION("Meta block cache (for extended attributes)");
MODULE_LICENSE("GPL");