From: Tejun Heo <tj@kernel.org>
To: Jan Kara <jack@suse.cz>
Cc: axboe@kernel.dk, hannes@cmpxchg.org, mhocko@kernel.org,
vdavydov.dev@gmail.com, cgroups@vger.kernel.org,
linux-mm@kvack.org, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org, kernel-team@fb.com, guro@fb.com,
akpm@linux-foundation.org
Subject: Re: [PATCH 5/5] writeback, memcg: Implement foreign dirty flushing
Date: Wed, 21 Aug 2019 09:00:37 -0700 [thread overview]
Message-ID: <20190821160037.GK2263813@devbig004.ftw2.facebook.com> (raw)
In-Reply-To: <20190816160256.GI3041@quack2.suse.cz>
Hello,
On Fri, Aug 16, 2019 at 06:02:56PM +0200, Jan Kara wrote:
> 1) You ask to writeback LONG_MAX pages. That means that you give up any
> livelock avoidance for the flusher work and you can writeback almost
> forever if someone is busily dirtying pages in the wb. I think you need to
> pick something like amount of dirty pages in the given wb (that would have
> to be fetched after everything is looked up) or just some arbitrary
> reasonably small constant like 1024 (but then I guess there's no guarantee
> stuck memcg will make any progress and you've invalidated the frn entry
> here).
I see. Yeah, I think the right thing to do would be feeding the
number of dirty pages or limiting it to one full sweep. I'll look
into it.
> 2) When you invalidate frn entry here by writing 0 to 'at', it's likely to get
> reused soon. Possibly while the writeback is still running. And then you
> won't start any writeback for the new entry because of the
> atomic_read(&frn->done.cnt) == 1 check. This seems like it could happen
> pretty frequently?
Hmm... yeah, the clearing might not make sense. I'll remove that.
Thanks.
--
tejun
next prev parent reply other threads:[~2019-08-21 16:00 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-15 19:56 [PATCHSET v2] writeback, memcg: Implement foreign inode flushing Tejun Heo
2019-08-15 19:57 ` [PATCH 1/5] writeback: Generalize and expose wb_completion Tejun Heo
2019-08-15 19:57 ` [PATCH 2/5] bdi: Add bdi->id Tejun Heo
2019-08-15 19:58 ` [PATCH 3/5] writeback: Separate out wb_get_lookup() from wb_get_create() Tejun Heo
2019-08-16 15:45 ` Jan Kara
2019-08-15 19:59 ` [PATCH 4/5] writeback, memcg: Implement cgroup_writeback_by_id() Tejun Heo
2019-08-16 15:47 ` Jan Kara
2019-08-21 21:02 ` [PATCH v3 " Tejun Heo
2019-08-26 13:49 ` Jan Kara
2019-08-15 19:59 ` [PATCH 5/5] writeback, memcg: Implement foreign dirty flushing Tejun Heo
2019-08-16 16:02 ` Jan Kara
2019-08-21 16:00 ` Tejun Heo [this message]
2019-08-21 16:04 ` Tejun Heo
2019-08-21 21:02 ` [PATCH v3 " Tejun Heo
2019-08-26 13:54 ` Jan Kara
2019-08-26 15:58 ` Tejun Heo
2019-08-26 16:06 [PATCHSET v3] writeback, memcg: Implement foreign inode flushing Tejun Heo
2019-08-26 16:06 ` [PATCH 5/5] writeback, memcg: Implement foreign dirty flushing Tejun Heo
2019-08-27 14:47 ` Jan Kara
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