From: Dennis Zhou <dennisszhou@gmail.com>
To: Jens Axboe <axboe@kernel.dk>, Tejun Heo <tj@kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Josef Bacik <josef@toxicpanda.com>
Cc: kernel-team@fb.com, linux-block@vger.kernel.org,
cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
"Dennis Zhou (Facebook)" <dennisszhou@gmail.com>
Subject: [PATCH 12/15] blkcg: cleanup and make blk_get_rl use blkg_lookup_create
Date: Thu, 30 Aug 2018 21:53:53 -0400 [thread overview]
Message-ID: <20180831015356.69796-13-dennisszhou@gmail.com> (raw)
In-Reply-To: <20180831015356.69796-1-dennisszhou@gmail.com>
From: "Dennis Zhou (Facebook)" <dennisszhou@gmail.com>
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>
---
include/linux/blk-cgroup.h | 53 ++++++++++++++++++++++++++------------
1 file changed, 37 insertions(+), 16 deletions(-)
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 3eed491e4daa..97cb82029b18 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -537,28 +537,49 @@ static inline struct request_list *blk_get_rl(struct request_queue *q,
rcu_read_lock();
- blkcg = bio_blkcg(bio);
- if (!blkcg)
+ blkg = bio->bi_blkg;
+ if (blkg) {
+ blkcg = bio->bi_blkg->blkcg;
+ if (blkcg == &blkcg_root)
+ goto rl_use_root;
+
+ blkg_get(blkg);
+ return &blkg->rl;
+ }
+
+ while (true) {
blkcg = css_to_blkcg(blkcg_css());
+ if (blkcg == &blkcg_root)
+ goto rl_use_root;
- /* bypass blkg lookup and use @q->root_rl directly for root */
- if (blkcg == &blkcg_root)
- goto root_rl;
+ blkg = blkg_lookup(blkcg, q);
- /*
- * 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;
+ if (unlikely(!blkg))
+ blkg = __blkg_lookup_create(blkcg, q);
+
+ if (IS_ERR(blkg)) {
+ if (PTR_ERR(blkg) == -ENODEV) {
+ cpu_relax();
+ continue;
+ } else {
+ goto rl_use_root;
+ }
+ }
+
+ if (blkg_try_get(blkg))
+ break;
+ cpu_relax();
+ }
- if (!blkg_try_get(blkg))
- goto root_rl;
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
next prev parent reply other threads:[~2018-08-31 1:54 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-31 1:53 [PATCH 00/15] blkcg ref count refactor/cleanup + blkcg avg_lat Dennis Zhou
2018-08-31 1:53 ` [PATCH 01/15] Revert "blk-throttle: fix race between blkcg_bio_issue_check() and cgroup_rmdir()" Dennis Zhou
2018-08-31 1:53 ` [PATCH 02/15] blkcg: delay blkg destruction until after writeback has finished Dennis Zhou
2018-08-31 15:27 ` Josef Bacik
2018-08-31 20:19 ` Dennis Zhou
2018-08-31 1:53 ` [PATCH 03/15] blkcg: use tryget logic when associating a blkg with a bio Dennis Zhou
2018-08-31 15:30 ` Josef Bacik
2018-08-31 20:20 ` Dennis Zhou
2018-08-31 1:53 ` [PATCH 04/15] blkcg: fix ref count issue with bio_blkcg using task_css Dennis Zhou
2018-08-31 15:35 ` Josef Bacik
2018-08-31 23:04 ` Tejun Heo
2018-09-06 15:21 ` Dennis Zhou
2018-08-31 1:53 ` [PATCH 05/15] blkcg: update blkg_lookup_create to do locking Dennis Zhou
2018-08-31 15:37 ` Josef Bacik
2018-08-31 23:09 ` Tejun Heo
2018-08-31 1:53 ` [PATCH 06/15] blkcg: always associate a bio with a blkg Dennis Zhou
2018-08-31 9:01 ` kbuild test robot
2018-08-31 10:02 ` kbuild test robot
2018-08-31 23:16 ` Tejun Heo
2018-09-06 20:41 ` Dennis Zhou
2018-09-07 3:03 ` [LKP] [blkcg] c02c58dab2: WARNING:at_block/blk-throttle.c:#blk_throtl_bio kernel test robot
2018-08-31 1:53 ` [PATCH 07/15] blkcg: consolidate bio_issue_init and blkg association Dennis Zhou
2018-08-31 9:19 ` kbuild test robot
2018-08-31 11:11 ` kbuild test robot
2018-08-31 15:42 ` Josef Bacik
2018-09-06 20:43 ` Dennis Zhou
2018-08-31 23:45 ` Tejun Heo
2018-08-31 1:53 ` [PATCH 08/15] blkcg: associate a blkg for pages being evicted by swap Dennis Zhou
2018-08-31 15:44 ` Josef Bacik
2018-08-31 23:47 ` Tejun Heo
2018-08-31 1:53 ` [PATCH 09/15] blkcg: associate writeback bios with a blkg Dennis Zhou
2018-08-31 15:45 ` Josef Bacik
2018-08-31 23:53 ` Tejun Heo
2018-08-31 1:53 ` [PATCH 10/15] blkcg: remove bio->bi_css and instead use bio->bi_blkg Dennis Zhou
2018-08-31 15:46 ` Josef Bacik
2018-09-01 0:13 ` Tejun Heo
2018-08-31 1:53 ` [PATCH 11/15] blkcg: remove additional reference to the css Dennis Zhou
2018-09-01 0:26 ` Tejun Heo
2018-09-06 20:45 ` Dennis Zhou
2018-08-31 1:53 ` Dennis Zhou [this message]
2018-09-01 0:29 ` [PATCH 12/15] blkcg: cleanup and make blk_get_rl use blkg_lookup_create Tejun Heo
2018-09-11 2:37 ` [LKP] [blkcg] 22f657e287: general_protection_fault:#[##] kernel test robot
2018-08-31 1:53 ` [PATCH 13/15] blkcg: change blkg reference counting to use percpu_ref Dennis Zhou
2018-08-31 15:49 ` Josef Bacik
2018-09-01 0:31 ` Tejun Heo
2018-09-06 20:46 ` Dennis Zhou
2018-09-07 3:08 ` [LKP] [blkcg] 6ef69a3a0b: WARNING:suspicious_RCU_usage kernel test robot
2018-08-31 1:53 ` [PATCH 14/15] blkcg: rename blkg_try_get to blkg_tryget Dennis Zhou
2018-08-31 15:50 ` Josef Bacik
2018-09-01 0:32 ` Tejun Heo
2018-08-31 1:53 ` [PATCH 15/15] blkcg: add average latency tracking to blk-cgroup Dennis Zhou
2018-08-31 10:22 ` kbuild test robot
2018-08-31 11:38 ` kbuild test robot
2018-09-01 0:35 ` [PATCH 00/15] blkcg ref count refactor/cleanup + blkcg avg_lat Tejun Heo
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