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Commit e2b09899 authored by Dennis Zhou (Facebook)'s avatar Dennis Zhou (Facebook) Committed by Jens Axboe
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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 <dennisszhou@gmail.com>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent f0fcb3ec

include/linux/blk-cgroup.h

+21 −13
Original line number Diff line number Diff line
@@ -586,28 +586,36 @@ static inline struct request_list *blk_get_rl(struct request_queue *q, 


	rcu_read_lock();



	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;



		blkg_get(bio->bi_blkg);

		rcu_read_unlock();

		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;



	rcu_read_unlock();

	return &blkg->rl;

root_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.

	 */

rl_use_root:

	rcu_read_unlock();

	return &q->root_rl;

}