aboutsummaryrefslogtreecommitdiff
path: root/lib/lru_cache.c
blob: 028f5d996eef64aa960546010e8321b1b0c5a369 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
/*
   lru_cache.c

   This file is part of DRBD by Philipp Reisner and Lars Ellenberg.

   Copyright (C) 2003-2008, LINBIT Information Technologies GmbH.
   Copyright (C) 2003-2008, Philipp Reisner <philipp.reisner@linbit.com>.
   Copyright (C) 2003-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.

   drbd is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   drbd is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with drbd; see the file COPYING.  If not, write to
   the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.

 */

#include <linux/module.h>
#include <linux/bitops.h>
#include <linux/slab.h>
#include <linux/string.h> /* for memset */
#include <linux/seq_file.h> /* for seq_printf */
#include <linux/lru_cache.h>

MODULE_AUTHOR("Philipp Reisner <phil@linbit.com>, "
	      "Lars Ellenberg <lars@linbit.com>");
MODULE_DESCRIPTION("lru_cache - Track sets of hot objects");
MODULE_LICENSE("GPL");

/* this is developers aid only.
 * it catches concurrent access (lack of locking on the users part) */
#define PARANOIA_ENTRY() do {		\
	BUG_ON(!lc);			\
	BUG_ON(!lc->nr_elements);	\
	BUG_ON(test_and_set_bit(__LC_PARANOIA, &lc->flags)); \
} while (0)

#define RETURN(x...)     do { \
	clear_bit_unlock(__LC_PARANOIA, &lc->flags); \
	return x ; } while (0)

/* BUG() if e is not one of the elements tracked by lc */
#define PARANOIA_LC_ELEMENT(lc, e) do {	\
	struct lru_cache *lc_ = (lc);	\
	struct lc_element *e_ = (e);	\
	unsigned i = e_->lc_index;	\
	BUG_ON(i >= lc_->nr_elements);	\
	BUG_ON(lc_->lc_element[i] != e_); } while (0)


/* We need to atomically
 *  - try to grab the lock (set LC_LOCKED)
 *  - only if there is no pending transaction
 *    (neither LC_DIRTY nor LC_STARVING is set)
 * Because of PARANOIA_ENTRY() above abusing lc->flags as well,
 * it is not sufficient to just say
 *	return 0 == cmpxchg(&lc->flags, 0, LC_LOCKED);
 */
int lc_try_lock(struct lru_cache *lc)
{
	unsigned long val;
	do {
		val = cmpxchg(&lc->flags, 0, LC_LOCKED);
	} while (unlikely (val == LC_PARANOIA));
	/* Spin until no-one is inside a PARANOIA_ENTRY()/RETURN() section. */
	return 0 == val;
#if 0
	/* Alternative approach, spin in case someone enters or leaves a
	 * PARANOIA_ENTRY()/RETURN() section. */
	unsigned long old, new, val;
	do {
		old = lc->flags & LC_PARANOIA;
		new = old | LC_LOCKED;
		val = cmpxchg(&lc->flags, old, new);
	} while (unlikely (val == (old ^ LC_PARANOIA)));
	return old == val;
#endif
}

/**
 * lc_create - prepares to track objects in an active set
 * @name: descriptive name only used in lc_seq_printf_stats and lc_seq_dump_details
 * @max_pending_changes: maximum changes to accumulate until a transaction is required
 * @e_count: number of elements allowed to be active simultaneously
 * @e_size: size of the tracked objects
 * @e_off: offset to the &struct lc_element member in a tracked object
 *
 * Returns a pointer to a newly initialized struct lru_cache on success,
 * or NULL on (allocation) failure.
 */
struct lru_cache *lc_create(const char *name, struct kmem_cache *cache,
		unsigned max_pending_changes,
		unsigned e_count, size_t e_size, size_t e_off)
{
	struct hlist_head *slot = NULL;
	struct lc_element **element = NULL;
	struct lru_cache *lc;
	struct lc_element *e;
	unsigned cache_obj_size = kmem_cache_size(cache);
	unsigned i;

	WARN_ON(cache_obj_size < e_size);
	if (cache_obj_size < e_size)
		return NULL;

	/* e_count too big; would probably fail the allocation below anyways.
	 * for typical use cases, e_count should be few thousand at most. */
	if (e_count > LC_MAX_ACTIVE)
		return NULL;

	slot = kcalloc(e_count, sizeof(struct hlist_head), GFP_KERNEL);
	if (!slot)
		goto out_fail;
	element = kzalloc(e_count * sizeof(struct lc_element *), GFP_KERNEL);
	if (!element)
		goto out_fail;

	lc = kzalloc(sizeof(*lc), GFP_KERNEL);
	if (!lc)
		goto out_fail;

	INIT_LIST_HEAD(&lc->in_use);
	INIT_LIST_HEAD(&lc->lru);
	INIT_LIST_HEAD(&lc->free);
	INIT_LIST_HEAD(&lc->to_be_changed);

	lc->name = name;
	lc->element_size = e_size;
	lc->element_off = e_off;
	lc->nr_elements = e_count;
	lc->max_pending_changes = max_pending_changes;
	lc->lc_cache = cache;
	lc->lc_element = element;
	lc->lc_slot = slot;

	/* preallocate all objects */
	for (i = 0; i < e_count; i++) {
		void *p = kmem_cache_alloc(cache, GFP_KERNEL);
		if (!p)
			break;
		memset(p, 0, lc->element_size);
		e = p + e_off;
		e->lc_index = i;
		e->lc_number = LC_FREE;
		e->lc_new_number = LC_FREE;
		list_add(&e->list, &lc->free);
		element[i] = e;
	}
	if (i == e_count)
		return lc;

	/* else: could not allocate all elements, give up */
	for (i--; i; i--) {
		void *p = element[i];
		kmem_cache_free(cache, p - e_off);
	}
	kfree(lc);
out_fail:
	kfree(element);
	kfree(slot);
	return NULL;
}

static void lc_free_by_index(struct lru_cache *lc, unsigned i)
{
	void *p = lc->lc_element[i];
	WARN_ON(!p);
	if (p) {
		p -= lc->element_off;
		kmem_cache_free(lc->lc_cache, p);
	}
}

/**
 * lc_destroy - frees memory allocated by lc_create()
 * @lc: the lru cache to destroy
 */
void lc_destroy(struct lru_cache *lc)
{
	unsigned i;
	if (!lc)
		return;
	for (i = 0; i < lc->nr_elements; i++)
		lc_free_by_index(lc, i);
	kfree(lc->lc_element);
	kfree(lc->lc_slot);
	kfree(lc);
}

/**
 * lc_reset - does a full reset for @lc and the hash table slots.
 * @lc: the lru cache to operate on
 *
 * It is roughly the equivalent of re-allocating a fresh lru_cache object,
 * basically a short cut to lc_destroy(lc); lc = lc_create(...);
 */
void lc_reset(struct lru_cache *lc)
{
	unsigned i;

	INIT_LIST_HEAD(&lc->in_use);
	INIT_LIST_HEAD(&lc->lru);
	INIT_LIST_HEAD(&lc->free);
	INIT_LIST_HEAD(&lc->to_be_changed);
	lc->used = 0;
	lc->hits = 0;
	lc->misses = 0;
	lc->starving = 0;
	lc->locked = 0;
	lc->changed = 0;
	lc->pending_changes = 0;
	lc->flags = 0;
	memset(lc->lc_slot, 0, sizeof(struct hlist_head) * lc->nr_elements);

	for (i = 0; i < lc->nr_elements; i++) {
		struct lc_element *e = lc->lc_element[i];
		void *p = e;
		p -= lc->element_off;
		memset(p, 0, lc->element_size);
		/* re-init it */
		e->lc_index = i;
		e->lc_number = LC_FREE;
		e->lc_new_number = LC_FREE;
		list_add(&e->list, &lc->free);
	}
}

/**
 * lc_seq_printf_stats - print stats about @lc into @seq
 * @seq: the seq_file to print into
 * @lc: the lru cache to print statistics of
 */
size_t lc_seq_printf_stats(struct seq_file *seq, struct lru_cache *lc)
{
	/* NOTE:
	 * total calls to lc_get are
	 * (starving + hits + misses)
	 * misses include "locked" count (update from an other thread in
	 * progress) and "changed", when this in fact lead to an successful
	 * update of the cache.
	 */
	seq_printf(seq, "\t%s: used:%u/%u hits:%lu misses:%lu starving:%lu locked:%lu changed:%lu\n",
		   lc->name, lc->used, lc->nr_elements,
		   lc->hits, lc->misses, lc->starving, lc->locked, lc->changed);

	return 0;
}

static struct hlist_head *lc_hash_slot(struct lru_cache *lc, unsigned int enr)
{
	return  lc->lc_slot + (enr % lc->nr_elements);
}


static struct lc_element *__lc_find(struct lru_cache *lc, unsigned int enr,
		bool include_changing)
{
	struct lc_element *e;

	BUG_ON(!lc);
	BUG_ON(!lc->nr_elements);
	hlist_for_each_entry(e, lc_hash_slot(lc, enr), colision) {
		/* "about to be changed" elements, pending transaction commit,
		 * are hashed by their "new number". "Normal" elements have
		 * lc_number == lc_new_number. */
		if (e->lc_new_number != enr)
			continue;
		if (e->lc_new_number == e->lc_number || include_changing)
			return e;
		break;
	}
	return NULL;
}

/**
 * lc_find - find element by label, if present in the hash table
 * @lc: The lru_cache object
 * @enr: element number
 *
 * Returns the pointer to an element, if the element with the requested
 * "label" or element number is present in the hash table,
 * or NULL if not found. Does not change the refcnt.
 * Ignores elements that are "about to be used", i.e. not yet in the active
 * set, but still pending transaction commit.
 */
struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr)
{
	return __lc_find(lc, enr, 0);
}

/**
 * lc_is_used - find element by label
 * @lc: The lru_cache object
 * @enr: element number
 *
 * Returns true, if the element with the requested "label" or element number is
 * present in the hash table, and is used (refcnt > 0).
 * Also finds elements that are not _currently_ used but only "about to be
 * used", i.e. on the "to_be_changed" list, pending transaction commit.
 */
bool lc_is_used(struct lru_cache *lc, unsigned int enr)
{
	struct lc_element *e = __lc_find(lc, enr, 1);
	return e && e->refcnt;
}

/**
 * lc_del - removes an element from the cache
 * @lc: The lru_cache object
 * @e: The element to remove
 *
 * @e must be unused (refcnt == 0). Moves @e from "lru" to "free" list,
 * sets @e->enr to %LC_FREE.
 */
void lc_del(struct lru_cache *lc, struct lc_element *e)
{
	PARANOIA_ENTRY();
	PARANOIA_LC_ELEMENT(lc, e);
	BUG_ON(e->refcnt);

	e->lc_number = e->lc_new_number = LC_FREE;
	hlist_del_init(&e->colision);
	list_move(&e->list, &lc->free);
	RETURN();
}

static struct lc_element *lc_prepare_for_change(struct lru_cache *lc, unsigned new_number)
{
	struct list_head *n;
	struct lc_element *e;

	if (!list_empty(&lc->free))
		n = lc->free.next;
	else if (!list_empty(&lc->lru))
		n = lc->lru.prev;
	else
		return NULL;

	e = list_entry(n, struct lc_element, list);
	PARANOIA_LC_ELEMENT(lc, e);

	e->lc_new_number = new_number;
	if (!hlist_unhashed(&e->colision))
		__hlist_del(&e->colision);
	hlist_add_head(&e->colision, lc_hash_slot(lc, new_number));
	list_move(&e->list, &lc->to_be_changed);

	return e;
}

static int lc_unused_element_available(struct lru_cache *lc)
{
	if (!list_empty(&lc->free))
		return 1; /* something on the free list */
	if (!list_empty(&lc->lru))
		return 1;  /* something to evict */

	return 0;
}

/* used as internal flags to __lc_get */
enum {
	LC_GET_MAY_CHANGE = 1,
	LC_GET_MAY_USE_UNCOMMITTED = 2,
};

static struct lc_element *__lc_get(struct lru_cache *lc, unsigned int enr, unsigned int flags)
{
	struct lc_element *e;

	PARANOIA_ENTRY();
	if (lc->flags & LC_STARVING) {
		++lc->starving;
		RETURN(NULL);
	}

	e = __lc_find(lc, enr, 1);
	/* if lc_new_number != lc_number,
	 * this enr is currently being pulled in already,
	 * and will be available once the pending transaction
	 * has been committed. */
	if (e) {
		if (e->lc_new_number != e->lc_number) {
			/* It has been found above, but on the "to_be_changed"
			 * list, not yet committed.  Don't pull it in twice,
			 * wait for the transaction, then try again...
			 */
			if (!(flags & LC_GET_MAY_USE_UNCOMMITTED))
				RETURN(NULL);
			/* ... unless the caller is aware of the implications,
			 * probably preparing a cumulative transaction. */
			++e->refcnt;
			++lc->hits;
			RETURN(e);
		}
		/* else: lc_new_number == lc_number; a real hit. */
		++lc->hits;
		if (e->refcnt++ == 0)
			lc->used++;
		list_move(&e->list, &lc->in_use); /* Not evictable... */
		RETURN(e);
	}
	/* e == NULL */

	++lc->misses;
	if (!(flags & LC_GET_MAY_CHANGE))
		RETURN(NULL);

	/* To avoid races with lc_try_lock(), first, mark us dirty
	 * (using test_and_set_bit, as it implies memory barriers), ... */
	test_and_set_bit(__LC_DIRTY, &lc->flags);

	/* ... only then check if it is locked anyways. If lc_unlock clears
	 * the dirty bit again, that's not a problem, we will come here again.
	 */
	if (test_bit(__LC_LOCKED, &lc->flags)) {
		++lc->locked;
		RETURN(NULL);
	}

	/* In case there is nothing available and we can not kick out
	 * the LRU element, we have to wait ...
	 */
	if (!lc_unused_element_available(lc)) {
		__set_bit(__LC_STARVING, &lc->flags);
		RETURN(NULL);
	}

	/* It was not present in the active set.  We are going to recycle an
	 * unused (or even "free") element, but we won't accumulate more than
	 * max_pending_changes changes.  */
	if (lc->pending_changes >= lc->max_pending_changes)
		RETURN(NULL);

	e = lc_prepare_for_change(lc, enr);
	BUG_ON(!e);

	clear_bit(__LC_STARVING, &lc->flags);
	BUG_ON(++e->refcnt != 1);
	lc->used++;
	lc->pending_changes++;

	RETURN(e);
}

/**
 * lc_get - get element by label, maybe change the active set
 * @lc: the lru cache to operate on
 * @enr: the label to look up
 *
 * Finds an element in the cache, increases its usage count,
 * "touches" and returns it.
 *
 * In case the requested number is not present, it needs to be added to the
 * cache. Therefore it is possible that an other element becomes evicted from
 * the cache. In either case, the user is notified so he is able to e.g. keep
 * a persistent log of the cache changes, and therefore the objects in use.
 *
 * Return values:
 *  NULL
 *     The cache was marked %LC_STARVING,
 *     or the requested label was not in the active set
 *     and a changing transaction is still pending (@lc was marked %LC_DIRTY).
 *     Or no unused or free element could be recycled (@lc will be marked as
 *     %LC_STARVING, blocking further lc_get() operations).
 *
 *  pointer to the element with the REQUESTED element number.
 *     In this case, it can be used right away
 *
 *  pointer to an UNUSED element with some different element number,
 *          where that different number may also be %LC_FREE.
 *
 *          In this case, the cache is marked %LC_DIRTY,
 *          so lc_try_lock() will no longer succeed.
 *          The returned element pointer is moved to the "to_be_changed" list,
 *          and registered with the new element number on the hash collision chains,
 *          so it is possible to pick it up from lc_is_used().
 *          Up to "max_pending_changes" (see lc_create()) can be accumulated.
 *          The user now should do whatever housekeeping is necessary,
 *          typically serialize on lc_try_lock_for_transaction(), then call
 *          lc_committed(lc) and lc_unlock(), to finish the change.
 *
 * NOTE: The user needs to check the lc_number on EACH use, so he recognizes
 *       any cache set change.
 */
struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
{
	return __lc_get(lc, enr, LC_GET_MAY_CHANGE);
}

/**
 * lc_get_cumulative - like lc_get; also finds to-be-changed elements
 * @lc: the lru cache to operate on
 * @enr: the label to look up
 *
 * Unlike lc_get this also returns the element for @enr, if it is belonging to
 * a pending transaction, so the return values are like for lc_get(),
 * plus:
 *
 * pointer to an element already on the "to_be_changed" list.
 * 	In this case, the cache was already marked %LC_DIRTY.
 *
 * Caller needs to make sure that the pending transaction is completed,
 * before proceeding to actually use this element.
 */
struct lc_element *lc_get_cumulative(struct lru_cache *lc, unsigned int enr)
{
	return __lc_get(lc, enr, LC_GET_MAY_CHANGE|LC_GET_MAY_USE_UNCOMMITTED);
}

/**
 * lc_try_get - get element by label, if present; do not change the active set
 * @lc: the lru cache to operate on
 * @enr: the label to look up
 *
 * Finds an element in the cache, increases its usage count,
 * "touches" and returns it.
 *
 * Return values:
 *  NULL
 *     The cache was marked %LC_STARVING,
 *     or the requested label was not in the active set
 *
 *  pointer to the element with the REQUESTED element number.
 *     In this case, it can be used right away
 */
struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr)
{
	return __lc_get(lc, enr, 0);
}

/**
 * lc_committed - tell @lc that pending changes have been recorded
 * @lc: the lru cache to operate on
 *
 * User is expected to serialize on explicit lc_try_lock_for_transaction()
 * before the transaction is started, and later needs to lc_unlock() explicitly
 * as well.
 */
void lc_committed(struct lru_cache *lc)
{
	struct lc_element *e, *tmp;

	PARANOIA_ENTRY();
	list_for_each_entry_safe(e, tmp, &lc->to_be_changed, list) {
		/* count number of changes, not number of transactions */
		++lc->changed;
		e->lc_number = e->lc_new_number;
		list_move(&e->list, &lc->in_use);
	}
	lc->pending_changes = 0;
	RETURN();
}


/**
 * lc_put - give up refcnt of @e
 * @lc: the lru cache to operate on
 * @e: the element to put
 *
 * If refcnt reaches zero, the element is moved to the lru list,
 * and a %LC_STARVING (if set) is cleared.
 * Returns the new (post-decrement) refcnt.
 */
unsigned int lc_put(struct lru_cache *lc, struct lc_element *e)
{
	PARANOIA_ENTRY();
	PARANOIA_LC_ELEMENT(lc, e);
	BUG_ON(e->refcnt == 0);
	BUG_ON(e->lc_number != e->lc_new_number);
	if (--e->refcnt == 0) {
		/* move it to the front of LRU. */
		list_move(&e->list, &lc->lru);
		lc->used--;
		clear_bit_unlock(__LC_STARVING, &lc->flags);
	}
	RETURN(e->refcnt);
}

/**
 * lc_element_by_index
 * @lc: the lru cache to operate on
 * @i: the index of the element to return
 */
struct lc_element *lc_element_by_index(struct lru_cache *lc, unsigned i)
{
	BUG_ON(i >= lc->nr_elements);
	BUG_ON(lc->lc_element[i] == NULL);
	BUG_ON(lc->lc_element[i]->lc_index != i);
	return lc->lc_element[i];
}

/**
 * lc_index_of
 * @lc: the lru cache to operate on
 * @e: the element to query for its index position in lc->element
 */
unsigned int lc_index_of(struct lru_cache *lc, struct lc_element *e)
{
	PARANOIA_LC_ELEMENT(lc, e);
	return e->lc_index;
}

/**
 * lc_set - associate index with label
 * @lc: the lru cache to operate on
 * @enr: the label to set
 * @index: the element index to associate label with.
 *
 * Used to initialize the active set to some previously recorded state.
 */
void lc_set(struct lru_cache *lc, unsigned int enr, int index)
{
	struct lc_element *e;
	struct list_head *lh;

	if (index < 0 || index >= lc->nr_elements)
		return;

	e = lc_element_by_index(lc, index);
	BUG_ON(e->lc_number != e->lc_new_number);
	BUG_ON(e->refcnt != 0);

	e->lc_number = e->lc_new_number = enr;
	hlist_del_init(&e->colision);
	if (enr == LC_FREE)
		lh = &lc->free;
	else {
		hlist_add_head(&e->colision, lc_hash_slot(lc, enr));
		lh = &lc->lru;
	}
	list_move(&e->list, lh);
}

/**
 * lc_dump - Dump a complete LRU cache to seq in textual form.
 * @lc: the lru cache to operate on
 * @seq: the &struct seq_file pointer to seq_printf into
 * @utext: user supplied additional "heading" or other info
 * @detail: function pointer the user may provide to dump further details
 * of the object the lc_element is embedded in. May be NULL.
 * Note: a leading space ' ' and trailing newline '\n' is implied.
 */
void lc_seq_dump_details(struct seq_file *seq, struct lru_cache *lc, char *utext,
	     void (*detail) (struct seq_file *, struct lc_element *))
{
	unsigned int nr_elements = lc->nr_elements;
	struct lc_element *e;
	int i;

	seq_printf(seq, "\tnn: lc_number (new nr) refcnt %s\n ", utext);
	for (i = 0; i < nr_elements; i++) {
		e = lc_element_by_index(lc, i);
		if (e->lc_number != e->lc_new_number)
			seq_printf(seq, "\t%5d: %6d %8d %6d ",
				i, e->lc_number, e->lc_new_number, e->refcnt);
		else
			seq_printf(seq, "\t%5d: %6d %-8s %6d ",
				i, e->lc_number, "-\"-", e->refcnt);
		if (detail)
			detail(seq, e);
		seq_putc(seq, '\n');
	}
}

EXPORT_SYMBOL(lc_create);
EXPORT_SYMBOL(lc_reset);
EXPORT_SYMBOL(lc_destroy);
EXPORT_SYMBOL(lc_set);
EXPORT_SYMBOL(lc_del);
EXPORT_SYMBOL(lc_try_get);
EXPORT_SYMBOL(lc_find);
EXPORT_SYMBOL(lc_get);
EXPORT_SYMBOL(lc_put);
EXPORT_SYMBOL(lc_committed);
EXPORT_SYMBOL(lc_element_by_index);
EXPORT_SYMBOL(lc_index_of);
EXPORT_SYMBOL(lc_seq_printf_stats);
EXPORT_SYMBOL(lc_seq_dump_details);
EXPORT_SYMBOL(lc_try_lock);
EXPORT_SYMBOL(lc_is_used);
EXPORT_SYMBOL(lc_get_cumulative);