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

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Message-ID: <20090421143130.GA22626@linux>
Date:	Tue, 21 Apr 2009 16:31:31 +0200
From:	Andrea Righi <righi.andrea@...il.com>
To:	Theodore Tso <tytso@....edu>
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 10:06:31AM -0400, Theodore Tso wrote:
> 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

Some months ago I posted a proposal to account, track and limit per
cgroup dirty pages in the memory cgroup subsystem:

https://lists.linux-foundation.org/pipermail/containers/2008-September/013140.html

At the moment I'm reworking on a similar and updated version. I know
that Kamezawa is also implementing something to account per cgroup dirty
pages in memory cgroup.

Moreover, io-throttle v14 already uses the page_cgroup structure to
encode into page_cgroup->flags the cgroup ID (io-throttle css_id()
actually) that originally dirtied the page.

This should be enough to track dirty pages and charge the right cgroup.

-Andrea
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