[PATCH 10/12] blkcg: cleanup and make blk_get_rl use blkg_lookup_create
From: Dennis Zhou <hidden>
Date: 2018-09-06 21:11:14
Also in:
cgroups, lkml
Subsystem:
block layer, control group - block io controller (blkio), the rest · Maintainers:
Jens Axboe, Tejun Heo, Josef Bacik, Linus Torvalds
From: "Dennis Zhou (Facebook)" <redacted> 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 <redacted> Acked-by: Tejun Heo <tj@kernel.org> --- include/linux/blk-cgroup.h | 36 ++++++++++++++++++++++-------------- 1 file changed, 22 insertions(+), 14 deletions(-)
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 2951ea3541b1..7964e7fc6521 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h@@ -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 */ - if (blkcg == &blkcg_root) - goto root_rl; + blkcg = css_to_blkcg(blkcg_css()); + if (blkg->blkcg == &blkcg_root) + 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; }
--
2.17.1