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Date: Tue, 21 Apr 2009 16:31:31 +0200
From: Andrea Righi <righi.andrea@gmail.com>
To: Theodore Tso <tytso@mit.edu>
Cc: Jens Axboe <jens.axboe@oracle.com>, Paul Menage <menage@google.com>,
       Balbir Singh <balbir@linux.vnet.ibm.com>,
       Gui Jianfeng <guijianfeng@cn.fujitsu.com>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, agk@sourceware.org,
       akpm@linux-foundation.org, baramsori72@gmail.com,
       Carl Henrik Lunde <chlunde@ping.uio.no>, dave@linux.vnet.ibm.com,
       Divyesh Shah <dpshah@google.com>, eric.rannaud@gmail.com,
       fernando@oss.ntt.co.jp, Hirokazu Takahashi <taka@valinux.co.jp>,
       Li Zefan <lizf@cn.fujitsu.com>, matt@bluehost.com,
       dradford@bluehost.com, ngupta@google.com, randy.dunlap@oracle.com,
       roberto@unbit.it, Ryo Tsuruta <ryov@valinux.co.jp>,
       Satoshi UCHIDA <s-uchida@ap.jp.nec.com>, subrata@linux.vnet.ibm.com,
       yoshikawa.takuya@oss.ntt.co.jp, containers@lists.linux-foundation.org,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH 9/9] ext3: do not throttle metadata and journal IO
Message-ID: <20090421143130.GA22626@linux>
References: <1239740480-28125-1-git-send-email-righi.andrea@gmail.com> <1239740480-28125-10-git-send-email-righi.andrea@gmail.com> <20090417123805.GC7117@mit.edu> <20090417125004.GY4593@kernel.dk> <20090417143903.GA30365@linux> <20090421001822.GB19186@mit.edu> <20090421083001.GA8441@linux> <20090421140631.GF19186@mit.edu>
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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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