linux-kernel - Re: [PATCH 18/23] io-controller: blkio_cgroup patches from Ryo to track async bios.

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Message-Id: <20090902095912.cdf8a55e.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 2 Sep 2009 09:59:12 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Ryo Tsuruta <ryov@...inux.co.jp>, dhaval@...ux.vnet.ibm.com,
	dm-devel@...hat.com, jens.axboe@...cle.com, agk@...hat.com,
	balbir@...ux.vnet.ibm.com, paolo.valente@...more.it,
	jmarchan@...hat.com, fernando@....ntt.co.jp, jmoyer@...hat.com,
	mingo@...e.hu, riel@...hat.com, fchecconi@...il.com,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	righi.andrea@...il.com, torvalds@...ux-foundation.org
Subject: Re: [PATCH 18/23] io-controller: blkio_cgroup patches from Ryo to
 track async bios.

On Tue, 1 Sep 2009 10:11:42 -0400
Vivek Goyal <vgoyal@...hat.com> wrote:
> > > > - Somebody also gave an example where there is a memory hogging process and
> > > >  possibly pushes out some processes to swap. It does not sound fair to
> > > >  charge those proccess for that swap writeout. These processes never
> > > >  requested swap IO.
> > 
> > I think that swap writeouts should be charged to the memory hogging
> > process, because the process consumes more resources and it should get
> > a penalty.
> > 
> 
> A process requesting memory gets IO penalty? IMHO, swapping is a kernel 
> mechanism and kernel's way of providing extended RAM. If we want to solve
> the issue of memory hogging by a process then right way to solve is to use
> memory controller and not by charging the process for IO activity.
> Instead, proabably a more suitable way is to charge swap activity to root
> group (where by default all the kernel related activity goes).   
> 

I agree. It't memcg's job.
(Support dirty_ratio in memcg is necessary, I think)

background-write-out-to-swap-for-memory-shortage should be handled
as kernel I/O. If swap-out-by-memcg bacause of its limit is a problem,
dirty_ratio for memcg should be implemetned.

Thanks,
-Kame

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