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>
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2 changed files with 47 additions and 10 deletions
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@ -256,6 +256,7 @@ extern void lc_destroy(struct lru_cache *lc);
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extern void lc_set(struct lru_cache *lc, unsigned int enr, int index);
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extern void lc_del(struct lru_cache *lc, struct lc_element *element);
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extern struct lc_element *lc_get_cumulative(struct lru_cache *lc, unsigned int enr);
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extern struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr);
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extern struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr);
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extern struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr);
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@ -365,7 +365,13 @@ static int lc_unused_element_available(struct lru_cache *lc)
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return 0;
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}
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static struct lc_element *__lc_get(struct lru_cache *lc, unsigned int enr, bool may_change)
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/* used as internal flags to __lc_get */
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enum {
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LC_GET_MAY_CHANGE = 1,
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LC_GET_MAY_USE_UNCOMMITTED = 2,
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};
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static struct lc_element *__lc_get(struct lru_cache *lc, unsigned int enr, unsigned int flags)
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{
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struct lc_element *e;
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@ -380,22 +386,31 @@ static struct lc_element *__lc_get(struct lru_cache *lc, unsigned int enr, bool
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* this enr is currently being pulled in already,
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* and will be available once the pending transaction
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* has been committed. */
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if (e && e->lc_new_number == e->lc_number) {
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if (e) {
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if (e->lc_new_number != e->lc_number) {
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/* It has been found above, but on the "to_be_changed"
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* list, not yet committed. Don't pull it in twice,
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* wait for the transaction, then try again...
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*/
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if (!(flags & LC_GET_MAY_USE_UNCOMMITTED))
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RETURN(NULL);
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/* ... unless the caller is aware of the implications,
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* probably preparing a cumulative transaction. */
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++e->refcnt;
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++lc->hits;
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RETURN(e);
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}
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/* else: lc_new_number == lc_number; a real hit. */
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++lc->hits;
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if (e->refcnt++ == 0)
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lc->used++;
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list_move(&e->list, &lc->in_use); /* Not evictable... */
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RETURN(e);
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}
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/* e == NULL */
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++lc->misses;
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if (!may_change)
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RETURN(NULL);
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/* It has been found above, but on the "to_be_changed" list, not yet
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* committed. Don't pull it in twice, wait for the transaction, then
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* try again */
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if (e)
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if (!(flags & LC_GET_MAY_CHANGE))
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RETURN(NULL);
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/* To avoid races with lc_try_lock(), first, mark us dirty
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@ -477,7 +492,27 @@ static struct lc_element *__lc_get(struct lru_cache *lc, unsigned int enr, bool
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*/
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struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
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{
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return __lc_get(lc, enr, 1);
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return __lc_get(lc, enr, LC_GET_MAY_CHANGE);
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}
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/**
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* lc_get_cumulative - like lc_get; also finds to-be-changed elements
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* @lc: the lru cache to operate on
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* @enr: the label to look up
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*
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* Unlike lc_get this also returns the element for @enr, if it is belonging to
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* a pending transaction, so the return values are like for lc_get(),
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* plus:
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*
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* pointer to an element already on the "to_be_changed" list.
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* In this case, the cache was already marked %LC_DIRTY.
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*
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* Caller needs to make sure that the pending transaction is completed,
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* before proceeding to actually use this element.
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*/
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struct lc_element *lc_get_cumulative(struct lru_cache *lc, unsigned int enr)
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{
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return __lc_get(lc, enr, LC_GET_MAY_CHANGE|LC_GET_MAY_USE_UNCOMMITTED);
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}
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/**
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@ -648,3 +683,4 @@ EXPORT_SYMBOL(lc_seq_printf_stats);
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EXPORT_SYMBOL(lc_seq_dump_details);
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EXPORT_SYMBOL(lc_try_lock);
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EXPORT_SYMBOL(lc_is_used);
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EXPORT_SYMBOL(lc_get_cumulative);
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