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authorLars Ellenberg <lars.ellenberg@linbit.com>2013-03-22 22:17:36 -0600
committerJens Axboe <axboe@kernel.dk>2013-03-22 22:17:36 -0600
commitcbe5e6109538ddab57764a88d9f0c2accd0c7d48 (patch)
treee09809862b9be7a44b44aa7367d470da14b2ccf0 /lib/lru_cache.c
parent779b3fe4c0e9dea19ae3ddef0b5fd1a663b63ee6 (diff)
downloadlinux-linaro-stable-cbe5e6109538ddab57764a88d9f0c2accd0c7d48.tar.gz
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>
Diffstat (limited to 'lib/lru_cache.c')
-rw-r--r--lib/lru_cache.c56
1 files changed, 46 insertions, 10 deletions
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);