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Date: Tue, 21 Apr 2009 10:06:31 -0400
From: Theodore Tso <tytso@mit.edu>
To: Andrea Righi <righi.andrea@gmail.com>
Cc: Jens Axboe <jens.axboe@oracle.com>, Paul Menage <menage@google.com>,
       Balbir Singh <balbir@linux.vnet.ibm.com>,
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Subject: Re: [PATCH 9/9] ext3: do not throttle metadata and journal IO
Message-ID: <20090421140631.GF19186@mit.edu>
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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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