linux-kernel - Re: [RFC 0/8] Cpuset aware writeback

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Date:	Wed, 17 Jan 2007 10:44:19 +1100
From:	David Chinner <dgc@....com>
To:	Andrew Morton <akpm@...l.org>
Cc:	Christoph Lameter <clameter@....com>, menage@...gle.com,
	linux-kernel@...r.kernel.org, nickpiggin@...oo.com.au,
	linux-mm@...ck.org, ak@...e.de, pj@....com, dgc@....com
Subject: Re: [RFC 0/8] Cpuset aware writeback

On Tue, Jan 16, 2007 at 01:53:25PM -0800, Andrew Morton wrote:
> > On Mon, 15 Jan 2007 21:47:43 -0800 (PST) Christoph Lameter
> > <clameter@....com> wrote:
> >
> > Currently cpusets are not able to do proper writeback since dirty ratio
> > calculations and writeback are all done for the system as a whole.
> 
> We _do_ do proper writeback.  But it's less efficient than it might be, and
> there's an NFS problem.
> 
> > This may result in a large percentage of a cpuset to become dirty without
> > writeout being triggered. Under NFS this can lead to OOM conditions.
> 
> OK, a big question: is this patchset a performance improvement or a
> correctness fix?  Given the above, and the lack of benchmark results I'm
> assuming it's for correctness.

Given that we've already got a 25-30% buffered write performance
degradation between 2.6.18 and 2.6.20-rc4 for simple sequential
write I/O to multiple filesystems concurrently, I'd really like
to see some serious I/O performance regression testing on this
change before it goes anywhere.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group
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