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authorLars Ellenberg2011-02-21 06:20:58 -0600
committerPhilipp Reisner2011-10-14 09:47:43 -0500
commita9efc748d679efb39fe7a8a536dde94cee691604 (patch)
tree0af3013566cd1d5aa638ed97ab18c7131791f17b /lib
parent0097f0405d365eff66235f887d47fa0b62b28599 (diff)
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lru_cache: consolidate lc_get and lc_try_get
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com> Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Diffstat (limited to 'lib')
-rw-r--r--lib/lru_cache.c120
1 files changed, 61 insertions, 59 deletions
diff --git a/lib/lru_cache.c b/lib/lru_cache.c
index 4f638b86674..17621684758 100644
--- a/lib/lru_cache.c
+++ b/lib/lru_cache.c
@@ -308,45 +308,7 @@ static int lc_unused_element_available(struct lru_cache *lc)
308 return 0; 308 return 0;
309} 309}
310 310
311 311static struct lc_element *__lc_get(struct lru_cache *lc, unsigned int enr, bool may_change)
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{ 312{
351 struct lc_element *e; 313 struct lc_element *e;
352 314
@@ -366,6 +328,8 @@ struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
366 } 328 }
367 329
368 ++lc->misses; 330 ++lc->misses;
331 if (!may_change)
332 RETURN(NULL);
369 333
370 /* In case there is nothing available and we can not kick out 334 /* In case there is nothing available and we can not kick out
371 * the LRU element, we have to wait ... 335 * the LRU element, we have to wait ...
@@ -397,29 +361,67 @@ struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
397 RETURN(e); 361 RETURN(e);
398} 362}
399 363
400/* similar to lc_get, 364/**
401 * but only gets a new reference on an existing element. 365 * lc_get - get element by label, maybe change the active set
402 * you either get the requested element, or NULL. 366 * @lc: the lru cache to operate on
403 * will be consolidated into one function. 367 * @enr: the label to look up
368 *
369 * Finds an element in the cache, increases its usage count,
370 * "touches" and returns it.
371 *
372 * In case the requested number is not present, it needs to be added to the
373 * cache. Therefore it is possible that an other element becomes evicted from
374 * the cache. In either case, the user is notified so he is able to e.g. keep
375 * a persistent log of the cache changes, and therefore the objects in use.
376 *
377 * Return values:
378 * NULL
379 * The cache was marked %LC_STARVING,
380 * or the requested label was not in the active set
381 * and a changing transaction is still pending (@lc was marked %LC_DIRTY).
382 * Or no unused or free element could be recycled (@lc will be marked as
383 * %LC_STARVING, blocking further lc_get() operations).
384 *
385 * pointer to the element with the REQUESTED element number.
386 * In this case, it can be used right away
387 *
388 * pointer to an UNUSED element with some different element number,
389 * where that different number may also be %LC_FREE.
390 *
391 * In this case, the cache is marked %LC_DIRTY (blocking further changes),
392 * and the returned element pointer is removed from the lru list and
393 * hash collision chains. The user now should do whatever housekeeping
394 * is necessary.
395 * Then he must call lc_changed(lc,element_pointer), to finish
396 * the change.
397 *
398 * NOTE: The user needs to check the lc_number on EACH use, so he recognizes
399 * any cache set change.
404 */ 400 */
405struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr) 401struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
406{ 402{
407 struct lc_element *e; 403 return __lc_get(lc, enr, 1);
408 404}
409 PARANOIA_ENTRY();
410 if (lc->flags & LC_STARVING) {
411 ++lc->starving;
412 RETURN(NULL);
413 }
414 405
415 e = lc_find(lc, enr); 406/**
416 if (e) { 407 * lc_try_get - get element by label, if present; do not change the active set
417 ++lc->hits; 408 * @lc: the lru cache to operate on
418 if (e->refcnt++ == 0) 409 * @enr: the label to look up
419 lc->used++; 410 *
420 list_move(&e->list, &lc->in_use); /* Not evictable... */ 411 * Finds an element in the cache, increases its usage count,
421 } 412 * "touches" and returns it.
422 RETURN(e); 413 *
414 * Return values:
415 * NULL
416 * The cache was marked %LC_STARVING,
417 * or the requested label was not in the active set
418 *
419 * pointer to the element with the REQUESTED element number.
420 * In this case, it can be used right away
421 */
422struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr)
423{
424 return __lc_get(lc, enr, 0);
423} 425}
424 426
425/** 427/**