linux-kernel - Re: [RFC] writeback and cgroup

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Message-ID: <20120418181836.GD2224@redhat.com>
Date:	Wed, 18 Apr 2012 14:18:36 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Jan Kara <jack@...e.cz>, Fengguang Wu <fengguang.wu@...el.com>,
	Jens Axboe <axboe@...nel.dk>, linux-mm@...ck.org,
	sjayaraman@...e.com, andrea@...terlinux.com, jmoyer@...hat.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	kamezawa.hiroyu@...fujitsu.com, lizefan@...wei.com,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	ctalbott@...gle.com, rni@...gle.com, lsf@...ts.linux-foundation.org
Subject: Re: [RFC] writeback and cgroup

On Tue, Apr 17, 2012 at 02:48:31PM -0700, Tejun Heo wrote:
[..]

> As for priority inversion through shared request pool, it is a problem
> which needs to be solved regardless of how async IOs are throttled.
> I'm not determined to which extent yet tho.  Different cgroups
> definitely need to be on separate pools but do we also want
> distinguish sync and async and what about ioprio?  Maybe we need a
> bybrid approach with larger common pool and reserved ones for each
> class?

currently we have global pool with separate limits for sync and async
and there is no consideration of ioprio. I think to keep it simple we
can just extend the same notion to keep per cgroup pool with internal
limits on sync/async requests to make sure sync IO does not get
serialized behind async IO. Personally I am not too worried about
async IO prio. It has never worked.

Thanks
Vivek
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