linux-kernel - Re: cgroup memory, blkio and the lovely swapping

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Message-Id: <20110304172430.19a3824a.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 4 Mar 2011 17:24:30 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Daniel Poelzleithner <poelzi@...lzi.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	containers@...ts.linux-foundation.org
Subject: Re: cgroup memory, blkio and the lovely swapping

On Fri, 4 Mar 2011 09:11:32 +0100
Daniel Poelzleithner <poelzi@...lzi.org> wrote:

> On Fri, 4 Mar 2011 16:54:55 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> 
> > Now, blkio cgroup does work only with synchronous I/O(direct I/O)
> > and never work with swap I/O. And I don't think swap-i/o limit
> > is a blkio matter.
> 
> I'm totally unsure about what subsystem it really belongs to. It is
> memory for sure, but disk access, which it actually affects, belongs to
> the blkio subsystem. Is there a technical reason why swap I/O is not run
> through the blkio system ?
> 

Now, blkio cgroup has no tags on each page. Then, it works only when
it can detect a thread which starts I/O in block layer.
But there is an activity to fix that.

http://marc.info/?l=linux-mm&m=129888823027871&w=2

I think you can discuss swap io handling in this thread.

> 
> > Memory cgroup is now developping dirty_ratio for memory cgroup.
> > By that, you can control the number of pages in writeback, in memory
> > cgroup. I think it will work for you.
> 
> I'm not sure that fixes the fairness problem on swapio. Just having a
> larger buffer before a writeback happens will reduce seeks, but not
> give fair share of io in swap in. It's good to control over it on
> cgroup level, but i doubt it will fix the problem.
> 

swap-in is out-of-control from memcg's view and have no plans.
IHMO, the number of swap-in will be blkio cgroup matter.

Thanks,
-Kame 

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