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From: Tejun Heo <tj@kernel.org>
To: Waiman Long <longman@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	cgroups@vger.kernel.org, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org, Ming Lei <ming.lei@redhat.com>
Subject: Re: [PATCH v2 2/2] blk-cgroup: Optimize blkcg_rstat_flush()
Date: Wed, 1 Jun 2022 11:28:43 -1000	[thread overview]
Message-ID: <YpfaC+wB5Th4tLDY@slm.duckdns.org> (raw)
In-Reply-To: <c26f153c-304c-e109-6626-bb8b79a2e2ad@redhat.com>

On Wed, Jun 01, 2022 at 05:25:53PM -0400, Waiman Long wrote:
> I think the best way to protect against blkg destruction is to get a percpu
> reference when put into lockless list and put it back when removed.
> 
> BTW, when I ran a test that continuously create and destroy containers, the
> total number of blkcg's kept on increasing. There are some freeing of
> blkcg's but no freeing of blkg's at all. Maybe we have a similar dying
> blkcg's problem here. I will take a further look at that when I have time.

They get pinned by per-cgroup writebacks which gets pinned by lingering page
cache and other remaining accounted memory areas, so I think they can hang
around if there's no memory pressure. But, yeah, it'd be great to verify
that they actually go away under memory pressure.

Thanks.

-- 
tejun

  reply	other threads:[~2022-06-01 21:28 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-01 16:53 [PATCH v2 1/2] blk-cgroup: Correctly free percpu iostat_cpu in blkg on error exit Waiman Long
2022-06-01 16:53 ` [PATCH v2 2/2] blk-cgroup: Optimize blkcg_rstat_flush() Waiman Long
2022-06-01 17:48   ` Tejun Heo
2022-06-01 18:15     ` Waiman Long
2022-06-01 18:35       ` Tejun Heo
2022-06-01 18:52         ` Waiman Long
2022-06-01 21:25           ` Waiman Long
2022-06-01 21:28             ` Tejun Heo [this message]
2022-06-01 21:32               ` Waiman Long
2022-06-02  1:52   ` kernel test robot
2022-06-01 17:48 ` [PATCH v2 1/2] blk-cgroup: Correctly free percpu iostat_cpu in blkg on error exit Tejun Heo

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