blkcg: cleanup and make blk_get_rl use blkg_lookup_create (e2b09899) · Commits · 戴 / test

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:

Dennis Zhou <dennisszhou@gmail.com> Acked-by:

Tejun Heo <tj@kernel.org> Signed-off-by:

Jens Axboe <axboe@kernel.dk>

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;
		}

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