Commit e2b09899 authored by Dennis Zhou (Facebook)'s avatar Dennis Zhou (Facebook) Committed by Jens Axboe

blkcg: cleanup and make blk_get_rl use blkg_lookup_create

blk_get_rl is responsible for identifying which request_list a request
should be allocated to. Try get logic was added earlier, but
semantically the logic was not changed.

This patch makes better use of the bio already having a reference to the
blkg in the hot path. The cold path uses a better fallback of
blkg_lookup_create rather than just blkg_lookup and then falling back to
the q->root_rl. If lookup_create fails with anything but -ENODEV, it
falls back to q->root_rl.

A clarifying comment is added to explain why q->root_rl is used rather
than the root blkg's rl.
Signed-off-by: default avatarDennis Zhou <>
Acked-by: default avatarTejun Heo <>
Signed-off-by: default avatarJens Axboe <>
parent f0fcb3ec
......@@ -586,28 +586,36 @@ static inline struct request_list *blk_get_rl(struct request_queue *q,
blkcg = bio_blkcg(bio);
if (!blkcg)
blkcg = css_to_blkcg(blkcg_css());
if (bio && bio->bi_blkg) {
blkcg = bio->bi_blkg->blkcg;
if (blkcg == &blkcg_root)
goto rl_use_root;
return &bio->bi_blkg->rl;
/* bypass blkg lookup and use @q->root_rl directly for root */
blkcg = css_to_blkcg(blkcg_css());
if (blkcg == &blkcg_root)
goto root_rl;
goto rl_use_root;
* Try to use blkg->rl. blkg lookup may fail under memory pressure
* or if either the blkcg or queue is going away. Fall back to
* root_rl in such cases.
blkg = blkg_lookup(blkcg, q);
if (unlikely(!blkg))
goto root_rl;
blkg = __blkg_lookup_create(blkcg, q);
if (!blkg_try_get(blkg))
goto root_rl;
goto rl_use_root;
return &blkg->rl;
* Each blkg has its own request_list, however, the root blkcg
* uses the request_queue's root_rl. This is to avoid most
* overhead for the root blkcg.
return &q->root_rl;
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