projects/linux·blob v3.4-rc7 · 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(__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);