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lru_cache: introduce lc_get_cumulative() 

New helper to be able to consolidate more updates
into a single transaction.
Without this, we can only grab a single refcount
on an updated element while preparing a transaction.

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.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

Fixed up by Jens to export lc_get_cumulative().

Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Lars Ellenberg 2013-03-22 22:17:36 -06:00 committed by Jens Axboe
parent 779b3fe4c0
commit cbe5e61095
2 changed files with 47 additions and 10 deletions
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1
include/linux/lru_cache.h
View File

@ -256,6 +256,7 @@ extern void lc_destroy(struct lru_cache *lc);
extern void lc_set(struct lru_cache *lc, unsigned int enr, int index);
extern void lc_del(struct lru_cache *lc, struct lc_element *element);
extern struct lc_element *lc_get_cumulative(struct lru_cache *lc, unsigned int enr);
extern struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr);
extern struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr);
extern struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr);

56
lib/lru_cache.c
View File

@ -365,7 +365,13 @@ static int lc_unused_element_available(struct lru_cache *lc)
return 0;
}
static struct lc_element *__lc_get(struct lru_cache *lc, unsigned int enr, bool may_change)
/* 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;
@ -380,22 +386,31 @@ static struct lc_element *__lc_get(struct lru_cache *lc, unsigned int enr, bool
* this enr is currently being pulled in already,
* and will be available once the pending transaction
* has been committed. */
if (e && e->lc_new_number == e->lc_number) {
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 (!may_change)
RETURN(NULL);
/* 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 (e)
if (!(flags & LC_GET_MAY_CHANGE))
RETURN(NULL);
/* To avoid races with lc_try_lock(), first, mark us dirty
@ -477,7 +492,27 @@ static struct lc_element *__lc_get(struct lru_cache *lc, unsigned int enr, bool
*/
struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
{
return __lc_get(lc, enr, 1);
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);
}
/**
@ -648,3 +683,4 @@ 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);