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: Dennis Zhou <dennisszhou@gmail.com> Acked-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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@ -586,28 +586,36 @@ static inline struct request_list *blk_get_rl(struct request_queue *q,
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rcu_read_lock();
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blkcg = bio_blkcg(bio);
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if (!blkcg)
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blkcg = css_to_blkcg(blkcg_css());
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if (bio && bio->bi_blkg) {
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blkcg = bio->bi_blkg->blkcg;
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if (blkcg == &blkcg_root)
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goto rl_use_root;
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/* bypass blkg lookup and use @q->root_rl directly for root */
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blkg_get(bio->bi_blkg);
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rcu_read_unlock();
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return &bio->bi_blkg->rl;
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}
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blkcg = css_to_blkcg(blkcg_css());
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if (blkcg == &blkcg_root)
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goto root_rl;
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goto rl_use_root;
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/*
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* Try to use blkg->rl. blkg lookup may fail under memory pressure
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* or if either the blkcg or queue is going away. Fall back to
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* root_rl in such cases.
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*/
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blkg = blkg_lookup(blkcg, q);
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if (unlikely(!blkg))
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goto root_rl;
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blkg = __blkg_lookup_create(blkcg, q);
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if (!blkg_try_get(blkg))
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goto root_rl;
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goto rl_use_root;
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rcu_read_unlock();
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return &blkg->rl;
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root_rl:
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/*
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* Each blkg has its own request_list, however, the root blkcg
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* uses the request_queue's root_rl. This is to avoid most
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* overhead for the root blkcg.
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*/
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rl_use_root:
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rcu_read_unlock();
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return &q->root_rl;
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}
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