From: Lars Ellenberg Date: Sat, 23 Mar 2013 04:17:36 +0000 (-0600) Subject: lru_cache: introduce lc_get_cumulative() X-Git-Tag: firefly_0821_release~3680^2~530^2~41 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=cbe5e6109538ddab57764a88d9f0c2accd0c7d48;p=firefly-linux-kernel-4.4.55.git 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 Signed-off-by: Lars Ellenberg Fixed up by Jens to export lc_get_cumulative(). Signed-off-by: Jens Axboe --- diff --git a/include/linux/lru_cache.h b/include/linux/lru_cache.h index 4019013c6593..46262284de47 100644 --- a/include/linux/lru_cache.h +++ b/include/linux/lru_cache.h @@ -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); diff --git a/lib/lru_cache.c b/lib/lru_cache.c index 8335d39d2ccd..4a83ecd03650 100644 --- a/lib/lru_cache.c +++ b/lib/lru_cache.c @@ -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);