linux-kernel - Re: [PATCH 9/9] ext3: do not throttle metadata and journal IO

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Message-ID: <20090421140631.GF19186@mit.edu>
Date:	Tue, 21 Apr 2009 10:06:31 -0400
From:	Theodore Tso <tytso@....edu>
To:	Andrea Righi <righi.andrea@...il.com>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	Paul Menage <menage@...gle.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Gui Jianfeng <guijianfeng@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	agk@...rceware.org, akpm@...ux-foundation.org,
	baramsori72@...il.com, Carl Henrik Lunde <chlunde@...g.uio.no>,
	dave@...ux.vnet.ibm.com, Divyesh Shah <dpshah@...gle.com>,
	eric.rannaud@...il.com, fernando@....ntt.co.jp,
	Hirokazu Takahashi <taka@...inux.co.jp>,
	Li Zefan <lizf@...fujitsu.com>, matt@...ehost.com,
	dradford@...ehost.com, ngupta@...gle.com, randy.dunlap@...cle.com,
	roberto@...it.it, Ryo Tsuruta <ryov@...inux.co.jp>,
	Satoshi UCHIDA <s-uchida@...jp.nec.com>,
	subrata@...ux.vnet.ibm.com, yoshikawa.takuya@....ntt.co.jp,
	containers@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 9/9] ext3: do not throttle metadata and journal IO

On Tue, Apr 21, 2009 at 10:30:02AM +0200, Andrea Righi wrote:
> 
> We're trying to address also this issue, setting max dirty pages limit
> per cgroup, and force a direct writeback when these limits are exceeded.
> 
> In this case dirty ratio throttling should happen automatically because
> the process will be throttled by the IO controller when it tries to
> writeback the dirty pages and submit IO requests.

The challenge here will be the accounting; consider that you may have
a file that had some of its pages in its page cache dirtied by a
process in cgroup A.  Now another process in cgroup B dirties some
more pages.  This could happen either via a mmap'ed file or via the
standard read/write system calls.  How do you track which dirty pages
should be charged against which cgroup?

							- Ted
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