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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 such as
the blkcg dying, request_queue is dying, or simply being OOM. 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.

Signed-off-by: Dennis Zhou <dennis@kernel.org>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Dennis Zhou
2018-12-05 12:10:28 -05:00
committed by Jens Axboe
parent b978962ad4
commit beea9da07d
5 changed files with 43 additions and 37 deletions
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4
block/blk-throttle.c
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@@ -2118,9 +2118,7 @@ static inline void throtl_update_latency_buckets(struct throtl_data *td)
static void blk_throtl_assoc_bio(struct throtl_grp *tg, struct bio *bio)
{
#ifdef CONFIG_BLK_DEV_THROTTLING_LOW
/* fallback to root_blkg if we fail to get a blkg ref */
if (bio->bi_css && (bio_associate_blkg(bio, tg_to_blkg(tg)) == -ENODEV))
bio_associate_blkg(bio, bio->bi_disk->queue->root_blkg);
bio_associate_blkg(bio, tg_to_blkg(tg));
bio_issue_init(&bio->bi_issue, bio_sectors(bio));
#endif
}