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blkcg: convert blkg_lookup_create to find closest blkg

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There are several scenarios where blkg_lookup_create can fail. Examples
include the blkcg dying, request_queue is dying, or simply being OOM. At
the end of the day, most handle this by simply falling back to the
q->root_blkg and calling it a day.

This patch implements the notion of closest blkg. During
blkg_lookup_create, if it fails to create, return the closest blkg
found or the q->root_blkg. blkg_try_get_closest is introduced and used
during association so a bio is always attached to a blkg.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Dennis Zhou <dennisszhou@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Dennis Zhou (Facebook)
2018-09-11 14:41:28 -04:00
committed by Jens Axboe
parent 49f4c2dc2b
commit 07b05bcc32
3 changed files with 40 additions and 14 deletions
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14
include/linux/blk-cgroup.h
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@@ -549,6 +549,20 @@ static inline struct blkcg_gq *blkg_try_get(struct blkcg_gq *blkg)
return NULL;
}
/**
* blkg_try_get_closest - try and get a blkg ref on the closet blkg
* @blkg: blkg to get
*
* This walks up the blkg tree to find the closest non-dying blkg and returns
* the blkg that it did association with as it may not be the passed in blkg.
*/
static inline struct blkcg_gq *blkg_try_get_closest(struct blkcg_gq *blkg)
{
while (!atomic_inc_not_zero(&blkg->refcnt))
blkg = blkg->parent;
return blkg;
}
void __blkg_release_rcu(struct rcu_head *rcu);