projects/linux·blob v3.17 · refs

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1/*
2 lru_cache.c
3
4 This file is part of DRBD by Philipp Reisner and Lars Ellenberg.
5
6 Copyright (C) 2003-2008, LINBIT Information Technologies GmbH.
7 Copyright (C) 2003-2008, Philipp Reisner <[email protected]>.
8 Copyright (C) 2003-2008, Lars Ellenberg <[email protected]>.
9
10 drbd is free software; you can redistribute it and/or modify
11 it under the terms of the GNU General Public License as published by
12 the Free Software Foundation; either version 2, or (at your option)
13 any later version.
14
15 drbd is distributed in the hope that it will be useful,
16 but WITHOUT ANY WARRANTY; without even the implied warranty of
17 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
18 GNU General Public License for more details.
19
20 You should have received a copy of the GNU General Public License
21 along with drbd; see the file COPYING. If not, write to
22 the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
23
24 */
25
26#include <linux/module.h>
27#include <linux/bitops.h>
28#include <linux/slab.h>
29#include <linux/string.h> /* for memset */
30#include <linux/seq_file.h> /* for seq_printf */
31#include <linux/lru_cache.h>
32
33MODULE_AUTHOR("Philipp Reisner <[email protected]>, "
34 "Lars Ellenberg <[email protected]>");
35MODULE_DESCRIPTION("lru_cache - Track sets of hot objects");
36MODULE_LICENSE("GPL");
37
38/* this is developers aid only.
39 * it catches concurrent access (lack of locking on the users part) */
40#define PARANOIA_ENTRY() do { \
41 BUG_ON(!lc); \
42 BUG_ON(!lc->nr_elements); \
43 BUG_ON(test_and_set_bit(__LC_PARANOIA, &lc->flags)); \
44} while (0)
45
46#define RETURN(x...) do { \
47 clear_bit_unlock(__LC_PARANOIA, &lc->flags); \
48 return x ; } while (0)
49
50/* BUG() if e is not one of the elements tracked by lc */
51#define PARANOIA_LC_ELEMENT(lc, e) do { \
52 struct lru_cache *lc_ = (lc); \
53 struct lc_element *e_ = (e); \
54 unsigned i = e_->lc_index; \
55 BUG_ON(i >= lc_->nr_elements); \
56 BUG_ON(lc_->lc_element[i] != e_); } while (0)
57
58
59/* We need to atomically
60 * - try to grab the lock (set LC_LOCKED)
61 * - only if there is no pending transaction
62 * (neither LC_DIRTY nor LC_STARVING is set)
63 * Because of PARANOIA_ENTRY() above abusing lc->flags as well,
64 * it is not sufficient to just say
65 * return 0 == cmpxchg(&lc->flags, 0, LC_LOCKED);
66 */
67int lc_try_lock(struct lru_cache *lc)
68{
69 unsigned long val;
70 do {
71 val = cmpxchg(&lc->flags, 0, LC_LOCKED);
72 } while (unlikely (val == LC_PARANOIA));
73 /* Spin until no-one is inside a PARANOIA_ENTRY()/RETURN() section. */
74 return 0 == val;
75#if 0
76 /* Alternative approach, spin in case someone enters or leaves a
77 * PARANOIA_ENTRY()/RETURN() section. */
78 unsigned long old, new, val;
79 do {
80 old = lc->flags & LC_PARANOIA;
81 new = old | LC_LOCKED;
82 val = cmpxchg(&lc->flags, old, new);
83 } while (unlikely (val == (old ^ LC_PARANOIA)));
84 return old == val;
85#endif
86}
87
88/**
89 * lc_create - prepares to track objects in an active set
90 * @name: descriptive name only used in lc_seq_printf_stats and lc_seq_dump_details
91 * @max_pending_changes: maximum changes to accumulate until a transaction is required
92 * @e_count: number of elements allowed to be active simultaneously
93 * @e_size: size of the tracked objects
94 * @e_off: offset to the &struct lc_element member in a tracked object
95 *
96 * Returns a pointer to a newly initialized struct lru_cache on success,
97 * or NULL on (allocation) failure.
98 */
99struct lru_cache *lc_create(const char *name, struct kmem_cache *cache,
100 unsigned max_pending_changes,
101 unsigned e_count, size_t e_size, size_t e_off)
102{
103 struct hlist_head *slot = NULL;
104 struct lc_element **element = NULL;
105 struct lru_cache *lc;
106 struct lc_element *e;
107 unsigned cache_obj_size = kmem_cache_size(cache);
108 unsigned i;
109
110 WARN_ON(cache_obj_size < e_size);
111 if (cache_obj_size < e_size)
112 return NULL;
113
114 /* e_count too big; would probably fail the allocation below anyways.
115 * for typical use cases, e_count should be few thousand at most. */
116 if (e_count > LC_MAX_ACTIVE)
117 return NULL;
118
119 slot = kcalloc(e_count, sizeof(struct hlist_head), GFP_KERNEL);
120 if (!slot)
121 goto out_fail;
122 element = kzalloc(e_count * sizeof(struct lc_element *), GFP_KERNEL);
123 if (!element)
124 goto out_fail;
125
126 lc = kzalloc(sizeof(*lc), GFP_KERNEL);
127 if (!lc)
128 goto out_fail;
129
130 INIT_LIST_HEAD(&lc->in_use);
131 INIT_LIST_HEAD(&lc->lru);
132 INIT_LIST_HEAD(&lc->free);
133 INIT_LIST_HEAD(&lc->to_be_changed);
134
135 lc->name = name;
136 lc->element_size = e_size;
137 lc->element_off = e_off;
138 lc->nr_elements = e_count;
139 lc->max_pending_changes = max_pending_changes;
140 lc->lc_cache = cache;
141 lc->lc_element = element;
142 lc->lc_slot = slot;
143
144 /* preallocate all objects */
145 for (i = 0; i < e_count; i++) {
146 void *p = kmem_cache_alloc(cache, GFP_KERNEL);
147 if (!p)
148 break;
149 memset(p, 0, lc->element_size);
150 e = p + e_off;
151 e->lc_index = i;
152 e->lc_number = LC_FREE;
153 e->lc_new_number = LC_FREE;
154 list_add(&e->list, &lc->free);
155 element[i] = e;
156 }
157 if (i == e_count)
158 return lc;
159
160 /* else: could not allocate all elements, give up */
161 for (i--; i; i--) {
162 void *p = element[i];
163 kmem_cache_free(cache, p - e_off);
164 }
165 kfree(lc);
166out_fail:
167 kfree(element);
168 kfree(slot);
169 return NULL;
170}
171
172static void lc_free_by_index(struct lru_cache *lc, unsigned i)
173{
174 void *p = lc->lc_element[i];
175 WARN_ON(!p);
176 if (p) {
177 p -= lc->element_off;
178 kmem_cache_free(lc->lc_cache, p);
179 }
180}
181
182/**
183 * lc_destroy - frees memory allocated by lc_create()
184 * @lc: the lru cache to destroy
185 */
186void lc_destroy(struct lru_cache *lc)
187{
188 unsigned i;
189 if (!lc)
190 return;
191 for (i = 0; i < lc->nr_elements; i++)
192 lc_free_by_index(lc, i);
193 kfree(lc->lc_element);
194 kfree(lc->lc_slot);
195 kfree(lc);
196}
197
198/**
199 * lc_reset - does a full reset for @lc and the hash table slots.
200 * @lc: the lru cache to operate on
201 *
202 * It is roughly the equivalent of re-allocating a fresh lru_cache object,
203 * basically a short cut to lc_destroy(lc); lc = lc_create(...);
204 */
205void lc_reset(struct lru_cache *lc)
206{
207 unsigned i;
208
209 INIT_LIST_HEAD(&lc->in_use);
210 INIT_LIST_HEAD(&lc->lru);
211 INIT_LIST_HEAD(&lc->free);
212 INIT_LIST_HEAD(&lc->to_be_changed);
213 lc->used = 0;
214 lc->hits = 0;
215 lc->misses = 0;
216 lc->starving = 0;
217 lc->locked = 0;
218 lc->changed = 0;
219 lc->pending_changes = 0;
220 lc->flags = 0;
221 memset(lc->lc_slot, 0, sizeof(struct hlist_head) * lc->nr_elements);
222
223 for (i = 0; i < lc->nr_elements; i++) {
224 struct lc_element *e = lc->lc_element[i];
225 void *p = e;
226 p -= lc->element_off;
227 memset(p, 0, lc->element_size);
228 /* re-init it */
229 e->lc_index = i;
230 e->lc_number = LC_FREE;
231 e->lc_new_number = LC_FREE;
232 list_add(&e->list, &lc->free);
233 }
234}
235
236/**
237 * lc_seq_printf_stats - print stats about @lc into @seq
238 * @seq: the seq_file to print into
239 * @lc: the lru cache to print statistics of
240 */
241size_t lc_seq_printf_stats(struct seq_file *seq, struct lru_cache *lc)
242{
243 /* NOTE:
244 * total calls to lc_get are
245 * (starving + hits + misses)
246 * misses include "locked" count (update from an other thread in
247 * progress) and "changed", when this in fact lead to an successful
248 * update of the cache.
249 */
250 return seq_printf(seq, "\t%s: used:%u/%u "
251 "hits:%lu misses:%lu starving:%lu locked:%lu changed:%lu\n",
252 lc->name, lc->used, lc->nr_elements,
253 lc->hits, lc->misses, lc->starving, lc->locked, lc->changed);
254}
255
256static struct hlist_head *lc_hash_slot(struct lru_cache *lc, unsigned int enr)
257{
258 return lc->lc_slot + (enr % lc->nr_elements);
259}
260
261
262static struct lc_element *__lc_find(struct lru_cache *lc, unsigned int enr,
263 bool include_changing)
264{
265 struct lc_element *e;
266
267 BUG_ON(!lc);
268 BUG_ON(!lc->nr_elements);
269 hlist_for_each_entry(e, lc_hash_slot(lc, enr), colision) {
270 /* "about to be changed" elements, pending transaction commit,
271 * are hashed by their "new number". "Normal" elements have
272 * lc_number == lc_new_number. */
273 if (e->lc_new_number != enr)
274 continue;
275 if (e->lc_new_number == e->lc_number || include_changing)
276 return e;
277 break;
278 }
279 return NULL;
280}
281
282/**
283 * lc_find - find element by label, if present in the hash table
284 * @lc: The lru_cache object
285 * @enr: element number
286 *
287 * Returns the pointer to an element, if the element with the requested
288 * "label" or element number is present in the hash table,
289 * or NULL if not found. Does not change the refcnt.
290 * Ignores elements that are "about to be used", i.e. not yet in the active
291 * set, but still pending transaction commit.
292 */
293struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr)
294{
295 return __lc_find(lc, enr, 0);
296}
297
298/**
299 * lc_is_used - find element by label
300 * @lc: The lru_cache object
301 * @enr: element number
302 *
303 * Returns true, if the element with the requested "label" or element number is
304 * present in the hash table, and is used (refcnt > 0).
305 * Also finds elements that are not _currently_ used but only "about to be
306 * used", i.e. on the "to_be_changed" list, pending transaction commit.
307 */
308bool lc_is_used(struct lru_cache *lc, unsigned int enr)
309{
310 struct lc_element *e = __lc_find(lc, enr, 1);
311 return e && e->refcnt;
312}
313
314/**
315 * lc_del - removes an element from the cache
316 * @lc: The lru_cache object
317 * @e: The element to remove
318 *
319 * @e must be unused (refcnt == 0). Moves @e from "lru" to "free" list,
320 * sets @e->enr to %LC_FREE.
321 */
322void lc_del(struct lru_cache *lc, struct lc_element *e)
323{
324 PARANOIA_ENTRY();
325 PARANOIA_LC_ELEMENT(lc, e);
326 BUG_ON(e->refcnt);
327
328 e->lc_number = e->lc_new_number = LC_FREE;
329 hlist_del_init(&e->colision);
330 list_move(&e->list, &lc->free);
331 RETURN();
332}
333
334static struct lc_element *lc_prepare_for_change(struct lru_cache *lc, unsigned new_number)
335{
336 struct list_head *n;
337 struct lc_element *e;
338
339 if (!list_empty(&lc->free))
340 n = lc->free.next;
341 else if (!list_empty(&lc->lru))
342 n = lc->lru.prev;
343 else
344 return NULL;
345
346 e = list_entry(n, struct lc_element, list);
347 PARANOIA_LC_ELEMENT(lc, e);
348
349 e->lc_new_number = new_number;
350 if (!hlist_unhashed(&e->colision))
351 __hlist_del(&e->colision);
352 hlist_add_head(&e->colision, lc_hash_slot(lc, new_number));
353 list_move(&e->list, &lc->to_be_changed);
354
355 return e;
356}
357
358static int lc_unused_element_available(struct lru_cache *lc)
359{
360 if (!list_empty(&lc->free))
361 return 1; /* something on the free list */
362 if (!list_empty(&lc->lru))
363 return 1; /* something to evict */
364
365 return 0;
366}
367
368/* used as internal flags to __lc_get */
369enum {
370 LC_GET_MAY_CHANGE = 1,
371 LC_GET_MAY_USE_UNCOMMITTED = 2,
372};
373
374static struct lc_element *__lc_get(struct lru_cache *lc, unsigned int enr, unsigned int flags)
375{
376 struct lc_element *e;
377
378 PARANOIA_ENTRY();
379 if (lc->flags & LC_STARVING) {
380 ++lc->starving;
381 RETURN(NULL);
382 }
383
384 e = __lc_find(lc, enr, 1);
385 /* if lc_new_number != lc_number,
386 * this enr is currently being pulled in already,
387 * and will be available once the pending transaction
388 * has been committed. */
389 if (e) {
390 if (e->lc_new_number != e->lc_number) {
391 /* It has been found above, but on the "to_be_changed"
392 * list, not yet committed. Don't pull it in twice,
393 * wait for the transaction, then try again...
394 */
395 if (!(flags & LC_GET_MAY_USE_UNCOMMITTED))
396 RETURN(NULL);
397 /* ... unless the caller is aware of the implications,
398 * probably preparing a cumulative transaction. */
399 ++e->refcnt;
400 ++lc->hits;
401 RETURN(e);
402 }
403 /* else: lc_new_number == lc_number; a real hit. */
404 ++lc->hits;
405 if (e->refcnt++ == 0)
406 lc->used++;
407 list_move(&e->list, &lc->in_use); /* Not evictable... */
408 RETURN(e);
409 }
410 /* e == NULL */
411
412 ++lc->misses;
413 if (!(flags & LC_GET_MAY_CHANGE))
414 RETURN(NULL);
415
416 /* To avoid races with lc_try_lock(), first, mark us dirty
417 * (using test_and_set_bit, as it implies memory barriers), ... */
418 test_and_set_bit(__LC_DIRTY, &lc->flags);
419
420 /* ... only then check if it is locked anyways. If lc_unlock clears
421 * the dirty bit again, that's not a problem, we will come here again.
422 */
423 if (test_bit(__LC_LOCKED, &lc->flags)) {
424 ++lc->locked;
425 RETURN(NULL);
426 }
427
428 /* In case there is nothing available and we can not kick out
429 * the LRU element, we have to wait ...
430 */
431 if (!lc_unused_element_available(lc)) {
432 __set_bit(__LC_STARVING, &lc->flags);
433 RETURN(NULL);
434 }
435
436 /* It was not present in the active set. We are going to recycle an
437 * unused (or even "free") element, but we won't accumulate more than
438 * max_pending_changes changes. */
439 if (lc->pending_changes >= lc->max_pending_changes)
440 RETURN(NULL);
441
442 e = lc_prepare_for_change(lc, enr);
443 BUG_ON(!e);
444
445 clear_bit(__LC_STARVING, &lc->flags);
446 BUG_ON(++e->refcnt != 1);
447 lc->used++;
448 lc->pending_changes++;
449
450 RETURN(e);
451}
452
453/**
454 * lc_get - get element by label, maybe change the active set
455 * @lc: the lru cache to operate on
456 * @enr: the label to look up
457 *
458 * Finds an element in the cache, increases its usage count,
459 * "touches" and returns it.
460 *
461 * In case the requested number is not present, it needs to be added to the
462 * cache. Therefore it is possible that an other element becomes evicted from
463 * the cache. In either case, the user is notified so he is able to e.g. keep
464 * a persistent log of the cache changes, and therefore the objects in use.
465 *
466 * Return values:
467 * NULL
468 * The cache was marked %LC_STARVING,
469 * or the requested label was not in the active set
470 * and a changing transaction is still pending (@lc was marked %LC_DIRTY).
471 * Or no unused or free element could be recycled (@lc will be marked as
472 * %LC_STARVING, blocking further lc_get() operations).
473 *
474 * pointer to the element with the REQUESTED element number.
475 * In this case, it can be used right away
476 *
477 * pointer to an UNUSED element with some different element number,
478 * where that different number may also be %LC_FREE.
479 *
480 * In this case, the cache is marked %LC_DIRTY,
481 * so lc_try_lock() will no longer succeed.
482 * The returned element pointer is moved to the "to_be_changed" list,
483 * and registered with the new element number on the hash collision chains,
484 * so it is possible to pick it up from lc_is_used().
485 * Up to "max_pending_changes" (see lc_create()) can be accumulated.
486 * The user now should do whatever housekeeping is necessary,
487 * typically serialize on lc_try_lock_for_transaction(), then call
488 * lc_committed(lc) and lc_unlock(), to finish the change.
489 *
490 * NOTE: The user needs to check the lc_number on EACH use, so he recognizes
491 * any cache set change.
492 */
493struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
494{
495 return __lc_get(lc, enr, LC_GET_MAY_CHANGE);
496}
497
498/**
499 * lc_get_cumulative - like lc_get; also finds to-be-changed elements
500 * @lc: the lru cache to operate on
501 * @enr: the label to look up
502 *
503 * Unlike lc_get this also returns the element for @enr, if it is belonging to
504 * a pending transaction, so the return values are like for lc_get(),
505 * plus:
506 *
507 * pointer to an element already on the "to_be_changed" list.
508 * In this case, the cache was already marked %LC_DIRTY.
509 *
510 * Caller needs to make sure that the pending transaction is completed,
511 * before proceeding to actually use this element.
512 */
513struct lc_element *lc_get_cumulative(struct lru_cache *lc, unsigned int enr)
514{
515 return __lc_get(lc, enr, LC_GET_MAY_CHANGE|LC_GET_MAY_USE_UNCOMMITTED);
516}
517
518/**
519 * lc_try_get - get element by label, if present; do not change the active set
520 * @lc: the lru cache to operate on
521 * @enr: the label to look up
522 *
523 * Finds an element in the cache, increases its usage count,
524 * "touches" and returns it.
525 *
526 * Return values:
527 * NULL
528 * The cache was marked %LC_STARVING,
529 * or the requested label was not in the active set
530 *
531 * pointer to the element with the REQUESTED element number.
532 * In this case, it can be used right away
533 */
534struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr)
535{
536 return __lc_get(lc, enr, 0);
537}
538
539/**
540 * lc_committed - tell @lc that pending changes have been recorded
541 * @lc: the lru cache to operate on
542 *
543 * User is expected to serialize on explicit lc_try_lock_for_transaction()
544 * before the transaction is started, and later needs to lc_unlock() explicitly
545 * as well.
546 */
547void lc_committed(struct lru_cache *lc)
548{
549 struct lc_element *e, *tmp;
550
551 PARANOIA_ENTRY();
552 list_for_each_entry_safe(e, tmp, &lc->to_be_changed, list) {
553 /* count number of changes, not number of transactions */
554 ++lc->changed;
555 e->lc_number = e->lc_new_number;
556 list_move(&e->list, &lc->in_use);
557 }
558 lc->pending_changes = 0;
559 RETURN();
560}
561
562
563/**
564 * lc_put - give up refcnt of @e
565 * @lc: the lru cache to operate on
566 * @e: the element to put
567 *
568 * If refcnt reaches zero, the element is moved to the lru list,
569 * and a %LC_STARVING (if set) is cleared.
570 * Returns the new (post-decrement) refcnt.
571 */
572unsigned int lc_put(struct lru_cache *lc, struct lc_element *e)
573{
574 PARANOIA_ENTRY();
575 PARANOIA_LC_ELEMENT(lc, e);
576 BUG_ON(e->refcnt == 0);
577 BUG_ON(e->lc_number != e->lc_new_number);
578 if (--e->refcnt == 0) {
579 /* move it to the front of LRU. */
580 list_move(&e->list, &lc->lru);
581 lc->used--;
582 clear_bit_unlock(__LC_STARVING, &lc->flags);
583 }
584 RETURN(e->refcnt);
585}
586
587/**
588 * lc_element_by_index
589 * @lc: the lru cache to operate on
590 * @i: the index of the element to return
591 */
592struct lc_element *lc_element_by_index(struct lru_cache *lc, unsigned i)
593{
594 BUG_ON(i >= lc->nr_elements);
595 BUG_ON(lc->lc_element[i] == NULL);
596 BUG_ON(lc->lc_element[i]->lc_index != i);
597 return lc->lc_element[i];
598}
599
600/**
601 * lc_index_of
602 * @lc: the lru cache to operate on
603 * @e: the element to query for its index position in lc->element
604 */
605unsigned int lc_index_of(struct lru_cache *lc, struct lc_element *e)
606{
607 PARANOIA_LC_ELEMENT(lc, e);
608 return e->lc_index;
609}
610
611/**
612 * lc_set - associate index with label
613 * @lc: the lru cache to operate on
614 * @enr: the label to set
615 * @index: the element index to associate label with.
616 *
617 * Used to initialize the active set to some previously recorded state.
618 */
619void lc_set(struct lru_cache *lc, unsigned int enr, int index)
620{
621 struct lc_element *e;
622 struct list_head *lh;
623
624 if (index < 0 || index >= lc->nr_elements)
625 return;
626
627 e = lc_element_by_index(lc, index);
628 BUG_ON(e->lc_number != e->lc_new_number);
629 BUG_ON(e->refcnt != 0);
630
631 e->lc_number = e->lc_new_number = enr;
632 hlist_del_init(&e->colision);
633 if (enr == LC_FREE)
634 lh = &lc->free;
635 else {
636 hlist_add_head(&e->colision, lc_hash_slot(lc, enr));
637 lh = &lc->lru;
638 }
639 list_move(&e->list, lh);
640}
641
642/**
643 * lc_dump - Dump a complete LRU cache to seq in textual form.
644 * @lc: the lru cache to operate on
645 * @seq: the &struct seq_file pointer to seq_printf into
646 * @utext: user supplied additional "heading" or other info
647 * @detail: function pointer the user may provide to dump further details
648 * of the object the lc_element is embedded in. May be NULL.
649 * Note: a leading space ' ' and trailing newline '\n' is implied.
650 */
651void lc_seq_dump_details(struct seq_file *seq, struct lru_cache *lc, char *utext,
652 void (*detail) (struct seq_file *, struct lc_element *))
653{
654 unsigned int nr_elements = lc->nr_elements;
655 struct lc_element *e;
656 int i;
657
658 seq_printf(seq, "\tnn: lc_number (new nr) refcnt %s\n ", utext);
659 for (i = 0; i < nr_elements; i++) {
660 e = lc_element_by_index(lc, i);
661 if (e->lc_number != e->lc_new_number)
662 seq_printf(seq, "\t%5d: %6d %8d %6d ",
663 i, e->lc_number, e->lc_new_number, e->refcnt);
664 else
665 seq_printf(seq, "\t%5d: %6d %-8s %6d ",
666 i, e->lc_number, "-\"-", e->refcnt);
667 if (detail)
668 detail(seq, e);
669 seq_putc(seq, '\n');
670 }
671}
672
673EXPORT_SYMBOL(lc_create);
674EXPORT_SYMBOL(lc_reset);
675EXPORT_SYMBOL(lc_destroy);
676EXPORT_SYMBOL(lc_set);
677EXPORT_SYMBOL(lc_del);
678EXPORT_SYMBOL(lc_try_get);
679EXPORT_SYMBOL(lc_find);
680EXPORT_SYMBOL(lc_get);
681EXPORT_SYMBOL(lc_put);
682EXPORT_SYMBOL(lc_committed);
683EXPORT_SYMBOL(lc_element_by_index);
684EXPORT_SYMBOL(lc_index_of);
685EXPORT_SYMBOL(lc_seq_printf_stats);
686EXPORT_SYMBOL(lc_seq_dump_details);
687EXPORT_SYMBOL(lc_try_lock);
688EXPORT_SYMBOL(lc_is_used);
689EXPORT_SYMBOL(lc_get_cumulative);