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v3.5.6
  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 <philipp.reisner@linbit.com>.
  8   Copyright (C) 2003-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.
  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 <phil@linbit.com>, "
 34	      "Lars Ellenberg <lars@linbit.com>");
 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(__LC_PARANOIA, &lc->flags); \
 48	smp_mb__after_clear_bit(); 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 * lc_create - prepares to track objects in an active set
 60 * @name: descriptive name only used in lc_seq_printf_stats and lc_seq_dump_details
 61 * @e_count: number of elements allowed to be active simultaneously
 62 * @e_size: size of the tracked objects
 63 * @e_off: offset to the &struct lc_element member in a tracked object
 64 *
 65 * Returns a pointer to a newly initialized struct lru_cache on success,
 66 * or NULL on (allocation) failure.
 67 */
 68struct lru_cache *lc_create(const char *name, struct kmem_cache *cache,
 69		unsigned e_count, size_t e_size, size_t e_off)
 70{
 71	struct hlist_head *slot = NULL;
 72	struct lc_element **element = NULL;
 73	struct lru_cache *lc;
 74	struct lc_element *e;
 75	unsigned cache_obj_size = kmem_cache_size(cache);
 76	unsigned i;
 77
 78	WARN_ON(cache_obj_size < e_size);
 79	if (cache_obj_size < e_size)
 80		return NULL;
 81
 82	/* e_count too big; would probably fail the allocation below anyways.
 83	 * for typical use cases, e_count should be few thousand at most. */
 84	if (e_count > LC_MAX_ACTIVE)
 85		return NULL;
 86
 87	slot = kcalloc(e_count, sizeof(struct hlist_head), GFP_KERNEL);
 88	if (!slot)
 89		goto out_fail;
 90	element = kzalloc(e_count * sizeof(struct lc_element *), GFP_KERNEL);
 91	if (!element)
 92		goto out_fail;
 93
 94	lc = kzalloc(sizeof(*lc), GFP_KERNEL);
 95	if (!lc)
 96		goto out_fail;
 97
 98	INIT_LIST_HEAD(&lc->in_use);
 99	INIT_LIST_HEAD(&lc->lru);
100	INIT_LIST_HEAD(&lc->free);
101
102	lc->name = name;
103	lc->element_size = e_size;
104	lc->element_off = e_off;
105	lc->nr_elements = e_count;
106	lc->new_number = LC_FREE;
107	lc->lc_cache = cache;
108	lc->lc_element = element;
109	lc->lc_slot = slot;
110
111	/* preallocate all objects */
112	for (i = 0; i < e_count; i++) {
113		void *p = kmem_cache_alloc(cache, GFP_KERNEL);
114		if (!p)
115			break;
116		memset(p, 0, lc->element_size);
117		e = p + e_off;
118		e->lc_index = i;
119		e->lc_number = LC_FREE;
120		list_add(&e->list, &lc->free);
121		element[i] = e;
122	}
123	if (i == e_count)
124		return lc;
125
126	/* else: could not allocate all elements, give up */
127	for (i--; i; i--) {
128		void *p = element[i];
129		kmem_cache_free(cache, p - e_off);
130	}
131	kfree(lc);
132out_fail:
133	kfree(element);
134	kfree(slot);
135	return NULL;
136}
137
138void lc_free_by_index(struct lru_cache *lc, unsigned i)
139{
140	void *p = lc->lc_element[i];
141	WARN_ON(!p);
142	if (p) {
143		p -= lc->element_off;
144		kmem_cache_free(lc->lc_cache, p);
145	}
146}
147
148/**
149 * lc_destroy - frees memory allocated by lc_create()
150 * @lc: the lru cache to destroy
151 */
152void lc_destroy(struct lru_cache *lc)
153{
154	unsigned i;
155	if (!lc)
156		return;
157	for (i = 0; i < lc->nr_elements; i++)
158		lc_free_by_index(lc, i);
159	kfree(lc->lc_element);
160	kfree(lc->lc_slot);
161	kfree(lc);
162}
163
164/**
165 * lc_reset - does a full reset for @lc and the hash table slots.
166 * @lc: the lru cache to operate on
167 *
168 * It is roughly the equivalent of re-allocating a fresh lru_cache object,
169 * basically a short cut to lc_destroy(lc); lc = lc_create(...);
170 */
171void lc_reset(struct lru_cache *lc)
172{
173	unsigned i;
174
175	INIT_LIST_HEAD(&lc->in_use);
176	INIT_LIST_HEAD(&lc->lru);
177	INIT_LIST_HEAD(&lc->free);
178	lc->used = 0;
179	lc->hits = 0;
180	lc->misses = 0;
181	lc->starving = 0;
182	lc->dirty = 0;
183	lc->changed = 0;
184	lc->flags = 0;
185	lc->changing_element = NULL;
186	lc->new_number = LC_FREE;
187	memset(lc->lc_slot, 0, sizeof(struct hlist_head) * lc->nr_elements);
188
189	for (i = 0; i < lc->nr_elements; i++) {
190		struct lc_element *e = lc->lc_element[i];
191		void *p = e;
192		p -= lc->element_off;
193		memset(p, 0, lc->element_size);
194		/* re-init it */
195		e->lc_index = i;
196		e->lc_number = LC_FREE;
197		list_add(&e->list, &lc->free);
198	}
199}
200
201/**
202 * lc_seq_printf_stats - print stats about @lc into @seq
203 * @seq: the seq_file to print into
204 * @lc: the lru cache to print statistics of
205 */
206size_t lc_seq_printf_stats(struct seq_file *seq, struct lru_cache *lc)
207{
208	/* NOTE:
209	 * total calls to lc_get are
210	 * (starving + hits + misses)
211	 * misses include "dirty" count (update from an other thread in
212	 * progress) and "changed", when this in fact lead to an successful
213	 * update of the cache.
214	 */
215	return seq_printf(seq, "\t%s: used:%u/%u "
216		"hits:%lu misses:%lu starving:%lu dirty:%lu changed:%lu\n",
217		lc->name, lc->used, lc->nr_elements,
218		lc->hits, lc->misses, lc->starving, lc->dirty, lc->changed);
219}
220
221static struct hlist_head *lc_hash_slot(struct lru_cache *lc, unsigned int enr)
222{
223	return  lc->lc_slot + (enr % lc->nr_elements);
224}
225
226
227/**
228 * lc_find - find element by label, if present in the hash table
229 * @lc: The lru_cache object
230 * @enr: element number
231 *
232 * Returns the pointer to an element, if the element with the requested
233 * "label" or element number is present in the hash table,
234 * or NULL if not found. Does not change the refcnt.
235 */
236struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr)
237{
238	struct hlist_node *n;
239	struct lc_element *e;
240
241	BUG_ON(!lc);
242	BUG_ON(!lc->nr_elements);
243	hlist_for_each_entry(e, n, lc_hash_slot(lc, enr), colision) {
244		if (e->lc_number == enr)
245			return e;
246	}
247	return NULL;
248}
249
250/* returned element will be "recycled" immediately */
251static struct lc_element *lc_evict(struct lru_cache *lc)
252{
253	struct list_head  *n;
254	struct lc_element *e;
255
256	if (list_empty(&lc->lru))
257		return NULL;
258
259	n = lc->lru.prev;
260	e = list_entry(n, struct lc_element, list);
261
262	PARANOIA_LC_ELEMENT(lc, e);
263
264	list_del(&e->list);
265	hlist_del(&e->colision);
266	return e;
267}
268
269/**
270 * lc_del - removes an element from the cache
271 * @lc: The lru_cache object
272 * @e: The element to remove
273 *
274 * @e must be unused (refcnt == 0). Moves @e from "lru" to "free" list,
275 * sets @e->enr to %LC_FREE.
276 */
277void lc_del(struct lru_cache *lc, struct lc_element *e)
278{
279	PARANOIA_ENTRY();
280	PARANOIA_LC_ELEMENT(lc, e);
281	BUG_ON(e->refcnt);
282
283	e->lc_number = LC_FREE;
284	hlist_del_init(&e->colision);
285	list_move(&e->list, &lc->free);
286	RETURN();
287}
288
289static struct lc_element *lc_get_unused_element(struct lru_cache *lc)
290{
291	struct list_head *n;
292
293	if (list_empty(&lc->free))
294		return lc_evict(lc);
295
296	n = lc->free.next;
297	list_del(n);
298	return list_entry(n, struct lc_element, list);
299}
300
301static int lc_unused_element_available(struct lru_cache *lc)
302{
303	if (!list_empty(&lc->free))
304		return 1; /* something on the free list */
305	if (!list_empty(&lc->lru))
306		return 1;  /* something to evict */
307
308	return 0;
309}
310
311
312/**
313 * lc_get - get element by label, maybe change the active set
314 * @lc: the lru cache to operate on
315 * @enr: the label to look up
316 *
317 * Finds an element in the cache, increases its usage count,
318 * "touches" and returns it.
319 *
320 * In case the requested number is not present, it needs to be added to the
321 * cache. Therefore it is possible that an other element becomes evicted from
322 * the cache. In either case, the user is notified so he is able to e.g. keep
323 * a persistent log of the cache changes, and therefore the objects in use.
324 *
325 * Return values:
326 *  NULL
327 *     The cache was marked %LC_STARVING,
328 *     or the requested label was not in the active set
329 *     and a changing transaction is still pending (@lc was marked %LC_DIRTY).
330 *     Or no unused or free element could be recycled (@lc will be marked as
331 *     %LC_STARVING, blocking further lc_get() operations).
332 *
333 *  pointer to the element with the REQUESTED element number.
334 *     In this case, it can be used right away
335 *
336 *  pointer to an UNUSED element with some different element number,
337 *          where that different number may also be %LC_FREE.
338 *
339 *          In this case, the cache is marked %LC_DIRTY (blocking further changes),
340 *          and the returned element pointer is removed from the lru list and
341 *          hash collision chains.  The user now should do whatever housekeeping
342 *          is necessary.
343 *          Then he must call lc_changed(lc,element_pointer), to finish
344 *          the change.
345 *
346 * NOTE: The user needs to check the lc_number on EACH use, so he recognizes
347 *       any cache set change.
348 */
349struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
350{
351	struct lc_element *e;
352
353	PARANOIA_ENTRY();
354	if (lc->flags & LC_STARVING) {
355		++lc->starving;
356		RETURN(NULL);
357	}
358
359	e = lc_find(lc, enr);
360	if (e) {
361		++lc->hits;
362		if (e->refcnt++ == 0)
363			lc->used++;
364		list_move(&e->list, &lc->in_use); /* Not evictable... */
365		RETURN(e);
366	}
367
368	++lc->misses;
369
370	/* In case there is nothing available and we can not kick out
371	 * the LRU element, we have to wait ...
372	 */
373	if (!lc_unused_element_available(lc)) {
374		__set_bit(__LC_STARVING, &lc->flags);
375		RETURN(NULL);
376	}
377
378	/* it was not present in the active set.
379	 * we are going to recycle an unused (or even "free") element.
380	 * user may need to commit a transaction to record that change.
381	 * we serialize on flags & TF_DIRTY */
382	if (test_and_set_bit(__LC_DIRTY, &lc->flags)) {
383		++lc->dirty;
384		RETURN(NULL);
385	}
386
387	e = lc_get_unused_element(lc);
388	BUG_ON(!e);
389
390	clear_bit(__LC_STARVING, &lc->flags);
391	BUG_ON(++e->refcnt != 1);
392	lc->used++;
393
394	lc->changing_element = e;
395	lc->new_number = enr;
396
397	RETURN(e);
398}
399
400/* similar to lc_get,
401 * but only gets a new reference on an existing element.
402 * you either get the requested element, or NULL.
403 * will be consolidated into one function.
404 */
405struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr)
406{
407	struct lc_element *e;
408
409	PARANOIA_ENTRY();
410	if (lc->flags & LC_STARVING) {
411		++lc->starving;
412		RETURN(NULL);
413	}
414
415	e = lc_find(lc, enr);
416	if (e) {
417		++lc->hits;
418		if (e->refcnt++ == 0)
419			lc->used++;
420		list_move(&e->list, &lc->in_use); /* Not evictable... */
421	}
422	RETURN(e);
423}
424
425/**
426 * lc_changed - tell @lc that the change has been recorded
427 * @lc: the lru cache to operate on
428 * @e: the element pending label change
429 */
430void lc_changed(struct lru_cache *lc, struct lc_element *e)
431{
432	PARANOIA_ENTRY();
433	BUG_ON(e != lc->changing_element);
434	PARANOIA_LC_ELEMENT(lc, e);
435	++lc->changed;
436	e->lc_number = lc->new_number;
437	list_add(&e->list, &lc->in_use);
438	hlist_add_head(&e->colision, lc_hash_slot(lc, lc->new_number));
439	lc->changing_element = NULL;
440	lc->new_number = LC_FREE;
441	clear_bit(__LC_DIRTY, &lc->flags);
442	smp_mb__after_clear_bit();
443	RETURN();
444}
445
446
447/**
448 * lc_put - give up refcnt of @e
449 * @lc: the lru cache to operate on
450 * @e: the element to put
451 *
452 * If refcnt reaches zero, the element is moved to the lru list,
453 * and a %LC_STARVING (if set) is cleared.
454 * Returns the new (post-decrement) refcnt.
455 */
456unsigned int lc_put(struct lru_cache *lc, struct lc_element *e)
457{
458	PARANOIA_ENTRY();
459	PARANOIA_LC_ELEMENT(lc, e);
460	BUG_ON(e->refcnt == 0);
461	BUG_ON(e == lc->changing_element);
462	if (--e->refcnt == 0) {
463		/* move it to the front of LRU. */
464		list_move(&e->list, &lc->lru);
465		lc->used--;
466		clear_bit(__LC_STARVING, &lc->flags);
467		smp_mb__after_clear_bit();
468	}
469	RETURN(e->refcnt);
470}
471
472/**
473 * lc_element_by_index
474 * @lc: the lru cache to operate on
475 * @i: the index of the element to return
476 */
477struct lc_element *lc_element_by_index(struct lru_cache *lc, unsigned i)
478{
479	BUG_ON(i >= lc->nr_elements);
480	BUG_ON(lc->lc_element[i] == NULL);
481	BUG_ON(lc->lc_element[i]->lc_index != i);
482	return lc->lc_element[i];
483}
484
485/**
486 * lc_index_of
487 * @lc: the lru cache to operate on
488 * @e: the element to query for its index position in lc->element
489 */
490unsigned int lc_index_of(struct lru_cache *lc, struct lc_element *e)
491{
492	PARANOIA_LC_ELEMENT(lc, e);
493	return e->lc_index;
494}
495
496/**
497 * lc_set - associate index with label
498 * @lc: the lru cache to operate on
499 * @enr: the label to set
500 * @index: the element index to associate label with.
501 *
502 * Used to initialize the active set to some previously recorded state.
503 */
504void lc_set(struct lru_cache *lc, unsigned int enr, int index)
505{
506	struct lc_element *e;
507
508	if (index < 0 || index >= lc->nr_elements)
509		return;
510
511	e = lc_element_by_index(lc, index);
512	e->lc_number = enr;
513
514	hlist_del_init(&e->colision);
515	hlist_add_head(&e->colision, lc_hash_slot(lc, enr));
516	list_move(&e->list, e->refcnt ? &lc->in_use : &lc->lru);
517}
518
519/**
520 * lc_dump - Dump a complete LRU cache to seq in textual form.
521 * @lc: the lru cache to operate on
522 * @seq: the &struct seq_file pointer to seq_printf into
523 * @utext: user supplied "heading" or other info
524 * @detail: function pointer the user may provide to dump further details
525 * of the object the lc_element is embedded in.
526 */
527void lc_seq_dump_details(struct seq_file *seq, struct lru_cache *lc, char *utext,
528	     void (*detail) (struct seq_file *, struct lc_element *))
529{
530	unsigned int nr_elements = lc->nr_elements;
531	struct lc_element *e;
532	int i;
533
534	seq_printf(seq, "\tnn: lc_number refcnt %s\n ", utext);
535	for (i = 0; i < nr_elements; i++) {
536		e = lc_element_by_index(lc, i);
537		if (e->lc_number == LC_FREE) {
538			seq_printf(seq, "\t%2d: FREE\n", i);
539		} else {
540			seq_printf(seq, "\t%2d: %4u %4u    ", i,
541				   e->lc_number, e->refcnt);
542			detail(seq, e);
543		}
544	}
545}
546
547EXPORT_SYMBOL(lc_create);
548EXPORT_SYMBOL(lc_reset);
549EXPORT_SYMBOL(lc_destroy);
550EXPORT_SYMBOL(lc_set);
551EXPORT_SYMBOL(lc_del);
552EXPORT_SYMBOL(lc_try_get);
553EXPORT_SYMBOL(lc_find);
554EXPORT_SYMBOL(lc_get);
555EXPORT_SYMBOL(lc_put);
556EXPORT_SYMBOL(lc_changed);
557EXPORT_SYMBOL(lc_element_by_index);
558EXPORT_SYMBOL(lc_index_of);
559EXPORT_SYMBOL(lc_seq_printf_stats);
560EXPORT_SYMBOL(lc_seq_dump_details);
v3.1
  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 <philipp.reisner@linbit.com>.
  8   Copyright (C) 2003-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.
  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 <phil@linbit.com>, "
 34	      "Lars Ellenberg <lars@linbit.com>");
 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(__LC_PARANOIA, &lc->flags); \
 48	smp_mb__after_clear_bit(); 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 * lc_create - prepares to track objects in an active set
 60 * @name: descriptive name only used in lc_seq_printf_stats and lc_seq_dump_details
 61 * @e_count: number of elements allowed to be active simultaneously
 62 * @e_size: size of the tracked objects
 63 * @e_off: offset to the &struct lc_element member in a tracked object
 64 *
 65 * Returns a pointer to a newly initialized struct lru_cache on success,
 66 * or NULL on (allocation) failure.
 67 */
 68struct lru_cache *lc_create(const char *name, struct kmem_cache *cache,
 69		unsigned e_count, size_t e_size, size_t e_off)
 70{
 71	struct hlist_head *slot = NULL;
 72	struct lc_element **element = NULL;
 73	struct lru_cache *lc;
 74	struct lc_element *e;
 75	unsigned cache_obj_size = kmem_cache_size(cache);
 76	unsigned i;
 77
 78	WARN_ON(cache_obj_size < e_size);
 79	if (cache_obj_size < e_size)
 80		return NULL;
 81
 82	/* e_count too big; would probably fail the allocation below anyways.
 83	 * for typical use cases, e_count should be few thousand at most. */
 84	if (e_count > LC_MAX_ACTIVE)
 85		return NULL;
 86
 87	slot = kcalloc(e_count, sizeof(struct hlist_head), GFP_KERNEL);
 88	if (!slot)
 89		goto out_fail;
 90	element = kzalloc(e_count * sizeof(struct lc_element *), GFP_KERNEL);
 91	if (!element)
 92		goto out_fail;
 93
 94	lc = kzalloc(sizeof(*lc), GFP_KERNEL);
 95	if (!lc)
 96		goto out_fail;
 97
 98	INIT_LIST_HEAD(&lc->in_use);
 99	INIT_LIST_HEAD(&lc->lru);
100	INIT_LIST_HEAD(&lc->free);
101
102	lc->name = name;
103	lc->element_size = e_size;
104	lc->element_off = e_off;
105	lc->nr_elements = e_count;
106	lc->new_number = LC_FREE;
107	lc->lc_cache = cache;
108	lc->lc_element = element;
109	lc->lc_slot = slot;
110
111	/* preallocate all objects */
112	for (i = 0; i < e_count; i++) {
113		void *p = kmem_cache_alloc(cache, GFP_KERNEL);
114		if (!p)
115			break;
116		memset(p, 0, lc->element_size);
117		e = p + e_off;
118		e->lc_index = i;
119		e->lc_number = LC_FREE;
120		list_add(&e->list, &lc->free);
121		element[i] = e;
122	}
123	if (i == e_count)
124		return lc;
125
126	/* else: could not allocate all elements, give up */
127	for (i--; i; i--) {
128		void *p = element[i];
129		kmem_cache_free(cache, p - e_off);
130	}
131	kfree(lc);
132out_fail:
133	kfree(element);
134	kfree(slot);
135	return NULL;
136}
137
138void lc_free_by_index(struct lru_cache *lc, unsigned i)
139{
140	void *p = lc->lc_element[i];
141	WARN_ON(!p);
142	if (p) {
143		p -= lc->element_off;
144		kmem_cache_free(lc->lc_cache, p);
145	}
146}
147
148/**
149 * lc_destroy - frees memory allocated by lc_create()
150 * @lc: the lru cache to destroy
151 */
152void lc_destroy(struct lru_cache *lc)
153{
154	unsigned i;
155	if (!lc)
156		return;
157	for (i = 0; i < lc->nr_elements; i++)
158		lc_free_by_index(lc, i);
159	kfree(lc->lc_element);
160	kfree(lc->lc_slot);
161	kfree(lc);
162}
163
164/**
165 * lc_reset - does a full reset for @lc and the hash table slots.
166 * @lc: the lru cache to operate on
167 *
168 * It is roughly the equivalent of re-allocating a fresh lru_cache object,
169 * basically a short cut to lc_destroy(lc); lc = lc_create(...);
170 */
171void lc_reset(struct lru_cache *lc)
172{
173	unsigned i;
174
175	INIT_LIST_HEAD(&lc->in_use);
176	INIT_LIST_HEAD(&lc->lru);
177	INIT_LIST_HEAD(&lc->free);
178	lc->used = 0;
179	lc->hits = 0;
180	lc->misses = 0;
181	lc->starving = 0;
182	lc->dirty = 0;
183	lc->changed = 0;
184	lc->flags = 0;
185	lc->changing_element = NULL;
186	lc->new_number = LC_FREE;
187	memset(lc->lc_slot, 0, sizeof(struct hlist_head) * lc->nr_elements);
188
189	for (i = 0; i < lc->nr_elements; i++) {
190		struct lc_element *e = lc->lc_element[i];
191		void *p = e;
192		p -= lc->element_off;
193		memset(p, 0, lc->element_size);
194		/* re-init it */
195		e->lc_index = i;
196		e->lc_number = LC_FREE;
197		list_add(&e->list, &lc->free);
198	}
199}
200
201/**
202 * lc_seq_printf_stats - print stats about @lc into @seq
203 * @seq: the seq_file to print into
204 * @lc: the lru cache to print statistics of
205 */
206size_t lc_seq_printf_stats(struct seq_file *seq, struct lru_cache *lc)
207{
208	/* NOTE:
209	 * total calls to lc_get are
210	 * (starving + hits + misses)
211	 * misses include "dirty" count (update from an other thread in
212	 * progress) and "changed", when this in fact lead to an successful
213	 * update of the cache.
214	 */
215	return seq_printf(seq, "\t%s: used:%u/%u "
216		"hits:%lu misses:%lu starving:%lu dirty:%lu changed:%lu\n",
217		lc->name, lc->used, lc->nr_elements,
218		lc->hits, lc->misses, lc->starving, lc->dirty, lc->changed);
219}
220
221static struct hlist_head *lc_hash_slot(struct lru_cache *lc, unsigned int enr)
222{
223	return  lc->lc_slot + (enr % lc->nr_elements);
224}
225
226
227/**
228 * lc_find - find element by label, if present in the hash table
229 * @lc: The lru_cache object
230 * @enr: element number
231 *
232 * Returns the pointer to an element, if the element with the requested
233 * "label" or element number is present in the hash table,
234 * or NULL if not found. Does not change the refcnt.
235 */
236struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr)
237{
238	struct hlist_node *n;
239	struct lc_element *e;
240
241	BUG_ON(!lc);
242	BUG_ON(!lc->nr_elements);
243	hlist_for_each_entry(e, n, lc_hash_slot(lc, enr), colision) {
244		if (e->lc_number == enr)
245			return e;
246	}
247	return NULL;
248}
249
250/* returned element will be "recycled" immediately */
251static struct lc_element *lc_evict(struct lru_cache *lc)
252{
253	struct list_head  *n;
254	struct lc_element *e;
255
256	if (list_empty(&lc->lru))
257		return NULL;
258
259	n = lc->lru.prev;
260	e = list_entry(n, struct lc_element, list);
261
262	PARANOIA_LC_ELEMENT(lc, e);
263
264	list_del(&e->list);
265	hlist_del(&e->colision);
266	return e;
267}
268
269/**
270 * lc_del - removes an element from the cache
271 * @lc: The lru_cache object
272 * @e: The element to remove
273 *
274 * @e must be unused (refcnt == 0). Moves @e from "lru" to "free" list,
275 * sets @e->enr to %LC_FREE.
276 */
277void lc_del(struct lru_cache *lc, struct lc_element *e)
278{
279	PARANOIA_ENTRY();
280	PARANOIA_LC_ELEMENT(lc, e);
281	BUG_ON(e->refcnt);
282
283	e->lc_number = LC_FREE;
284	hlist_del_init(&e->colision);
285	list_move(&e->list, &lc->free);
286	RETURN();
287}
288
289static struct lc_element *lc_get_unused_element(struct lru_cache *lc)
290{
291	struct list_head *n;
292
293	if (list_empty(&lc->free))
294		return lc_evict(lc);
295
296	n = lc->free.next;
297	list_del(n);
298	return list_entry(n, struct lc_element, list);
299}
300
301static int lc_unused_element_available(struct lru_cache *lc)
302{
303	if (!list_empty(&lc->free))
304		return 1; /* something on the free list */
305	if (!list_empty(&lc->lru))
306		return 1;  /* something to evict */
307
308	return 0;
309}
310
311
312/**
313 * lc_get - get element by label, maybe change the active set
314 * @lc: the lru cache to operate on
315 * @enr: the label to look up
316 *
317 * Finds an element in the cache, increases its usage count,
318 * "touches" and returns it.
319 *
320 * In case the requested number is not present, it needs to be added to the
321 * cache. Therefore it is possible that an other element becomes evicted from
322 * the cache. In either case, the user is notified so he is able to e.g. keep
323 * a persistent log of the cache changes, and therefore the objects in use.
324 *
325 * Return values:
326 *  NULL
327 *     The cache was marked %LC_STARVING,
328 *     or the requested label was not in the active set
329 *     and a changing transaction is still pending (@lc was marked %LC_DIRTY).
330 *     Or no unused or free element could be recycled (@lc will be marked as
331 *     %LC_STARVING, blocking further lc_get() operations).
332 *
333 *  pointer to the element with the REQUESTED element number.
334 *     In this case, it can be used right away
335 *
336 *  pointer to an UNUSED element with some different element number,
337 *          where that different number may also be %LC_FREE.
338 *
339 *          In this case, the cache is marked %LC_DIRTY (blocking further changes),
340 *          and the returned element pointer is removed from the lru list and
341 *          hash collision chains.  The user now should do whatever housekeeping
342 *          is necessary.
343 *          Then he must call lc_changed(lc,element_pointer), to finish
344 *          the change.
345 *
346 * NOTE: The user needs to check the lc_number on EACH use, so he recognizes
347 *       any cache set change.
348 */
349struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
350{
351	struct lc_element *e;
352
353	PARANOIA_ENTRY();
354	if (lc->flags & LC_STARVING) {
355		++lc->starving;
356		RETURN(NULL);
357	}
358
359	e = lc_find(lc, enr);
360	if (e) {
361		++lc->hits;
362		if (e->refcnt++ == 0)
363			lc->used++;
364		list_move(&e->list, &lc->in_use); /* Not evictable... */
365		RETURN(e);
366	}
367
368	++lc->misses;
369
370	/* In case there is nothing available and we can not kick out
371	 * the LRU element, we have to wait ...
372	 */
373	if (!lc_unused_element_available(lc)) {
374		__set_bit(__LC_STARVING, &lc->flags);
375		RETURN(NULL);
376	}
377
378	/* it was not present in the active set.
379	 * we are going to recycle an unused (or even "free") element.
380	 * user may need to commit a transaction to record that change.
381	 * we serialize on flags & TF_DIRTY */
382	if (test_and_set_bit(__LC_DIRTY, &lc->flags)) {
383		++lc->dirty;
384		RETURN(NULL);
385	}
386
387	e = lc_get_unused_element(lc);
388	BUG_ON(!e);
389
390	clear_bit(__LC_STARVING, &lc->flags);
391	BUG_ON(++e->refcnt != 1);
392	lc->used++;
393
394	lc->changing_element = e;
395	lc->new_number = enr;
396
397	RETURN(e);
398}
399
400/* similar to lc_get,
401 * but only gets a new reference on an existing element.
402 * you either get the requested element, or NULL.
403 * will be consolidated into one function.
404 */
405struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr)
406{
407	struct lc_element *e;
408
409	PARANOIA_ENTRY();
410	if (lc->flags & LC_STARVING) {
411		++lc->starving;
412		RETURN(NULL);
413	}
414
415	e = lc_find(lc, enr);
416	if (e) {
417		++lc->hits;
418		if (e->refcnt++ == 0)
419			lc->used++;
420		list_move(&e->list, &lc->in_use); /* Not evictable... */
421	}
422	RETURN(e);
423}
424
425/**
426 * lc_changed - tell @lc that the change has been recorded
427 * @lc: the lru cache to operate on
428 * @e: the element pending label change
429 */
430void lc_changed(struct lru_cache *lc, struct lc_element *e)
431{
432	PARANOIA_ENTRY();
433	BUG_ON(e != lc->changing_element);
434	PARANOIA_LC_ELEMENT(lc, e);
435	++lc->changed;
436	e->lc_number = lc->new_number;
437	list_add(&e->list, &lc->in_use);
438	hlist_add_head(&e->colision, lc_hash_slot(lc, lc->new_number));
439	lc->changing_element = NULL;
440	lc->new_number = LC_FREE;
441	clear_bit(__LC_DIRTY, &lc->flags);
442	smp_mb__after_clear_bit();
443	RETURN();
444}
445
446
447/**
448 * lc_put - give up refcnt of @e
449 * @lc: the lru cache to operate on
450 * @e: the element to put
451 *
452 * If refcnt reaches zero, the element is moved to the lru list,
453 * and a %LC_STARVING (if set) is cleared.
454 * Returns the new (post-decrement) refcnt.
455 */
456unsigned int lc_put(struct lru_cache *lc, struct lc_element *e)
457{
458	PARANOIA_ENTRY();
459	PARANOIA_LC_ELEMENT(lc, e);
460	BUG_ON(e->refcnt == 0);
461	BUG_ON(e == lc->changing_element);
462	if (--e->refcnt == 0) {
463		/* move it to the front of LRU. */
464		list_move(&e->list, &lc->lru);
465		lc->used--;
466		clear_bit(__LC_STARVING, &lc->flags);
467		smp_mb__after_clear_bit();
468	}
469	RETURN(e->refcnt);
470}
471
472/**
473 * lc_element_by_index
474 * @lc: the lru cache to operate on
475 * @i: the index of the element to return
476 */
477struct lc_element *lc_element_by_index(struct lru_cache *lc, unsigned i)
478{
479	BUG_ON(i >= lc->nr_elements);
480	BUG_ON(lc->lc_element[i] == NULL);
481	BUG_ON(lc->lc_element[i]->lc_index != i);
482	return lc->lc_element[i];
483}
484
485/**
486 * lc_index_of
487 * @lc: the lru cache to operate on
488 * @e: the element to query for its index position in lc->element
489 */
490unsigned int lc_index_of(struct lru_cache *lc, struct lc_element *e)
491{
492	PARANOIA_LC_ELEMENT(lc, e);
493	return e->lc_index;
494}
495
496/**
497 * lc_set - associate index with label
498 * @lc: the lru cache to operate on
499 * @enr: the label to set
500 * @index: the element index to associate label with.
501 *
502 * Used to initialize the active set to some previously recorded state.
503 */
504void lc_set(struct lru_cache *lc, unsigned int enr, int index)
505{
506	struct lc_element *e;
507
508	if (index < 0 || index >= lc->nr_elements)
509		return;
510
511	e = lc_element_by_index(lc, index);
512	e->lc_number = enr;
513
514	hlist_del_init(&e->colision);
515	hlist_add_head(&e->colision, lc_hash_slot(lc, enr));
516	list_move(&e->list, e->refcnt ? &lc->in_use : &lc->lru);
517}
518
519/**
520 * lc_dump - Dump a complete LRU cache to seq in textual form.
521 * @lc: the lru cache to operate on
522 * @seq: the &struct seq_file pointer to seq_printf into
523 * @utext: user supplied "heading" or other info
524 * @detail: function pointer the user may provide to dump further details
525 * of the object the lc_element is embedded in.
526 */
527void lc_seq_dump_details(struct seq_file *seq, struct lru_cache *lc, char *utext,
528	     void (*detail) (struct seq_file *, struct lc_element *))
529{
530	unsigned int nr_elements = lc->nr_elements;
531	struct lc_element *e;
532	int i;
533
534	seq_printf(seq, "\tnn: lc_number refcnt %s\n ", utext);
535	for (i = 0; i < nr_elements; i++) {
536		e = lc_element_by_index(lc, i);
537		if (e->lc_number == LC_FREE) {
538			seq_printf(seq, "\t%2d: FREE\n", i);
539		} else {
540			seq_printf(seq, "\t%2d: %4u %4u    ", i,
541				   e->lc_number, e->refcnt);
542			detail(seq, e);
543		}
544	}
545}
546
547EXPORT_SYMBOL(lc_create);
548EXPORT_SYMBOL(lc_reset);
549EXPORT_SYMBOL(lc_destroy);
550EXPORT_SYMBOL(lc_set);
551EXPORT_SYMBOL(lc_del);
552EXPORT_SYMBOL(lc_try_get);
553EXPORT_SYMBOL(lc_find);
554EXPORT_SYMBOL(lc_get);
555EXPORT_SYMBOL(lc_put);
556EXPORT_SYMBOL(lc_changed);
557EXPORT_SYMBOL(lc_element_by_index);
558EXPORT_SYMBOL(lc_index_of);
559EXPORT_SYMBOL(lc_seq_printf_stats);
560EXPORT_SYMBOL(lc_seq_dump_details);