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

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Message-ID: <20120405163854.GE12854@google.com>
Date:	Thu, 5 Apr 2012 09:38:54 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Fengguang Wu <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	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

Hey, Vivek.

On Wed, Apr 04, 2012 at 11:49:09AM -0700, Tejun Heo wrote:
> > I am not sure what are you trying to say here. But primarily blk-throttle
> > will throttle read and direct IO. Buffered writes will go to root cgroup
> > which is typically unthrottled.
> 
> Ooh, my bad then.  Anyways, then the same applies to blk-throttle.
> Our current implementation essentially collapses at the face of
> write-heavy workload.

I went through the code and couldn't find where blk-throttle is
discriminating async IOs.  Were you saying that blk-throttle currently
doesn't throttle because those IOs aren't associated with the dirtying
task?  If so, note that it's different from cfq which explicitly
assigns all async IOs when choosing cfqq even if we fix tagging.

Thanks.

-- 
tejun
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