linux-kernel - Re: [REGRESSION] 2.6.19/2.6.20-rc3 buffered write slowdown

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Date:	Thu, 11 Jan 2007 10:18:48 +1100
From:	David Chinner <dgc@....com>
To:	Christoph Lameter <clameter@....com>
Cc:	David Chinner <dgc@....com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [REGRESSION] 2.6.19/2.6.20-rc3 buffered write slowdown

On Wed, Jan 10, 2007 at 03:12:02PM -0800, Christoph Lameter wrote:
> On Thu, 11 Jan 2007, David Chinner wrote:
> 
> > Well, pdflush appears to be doing very little on both 2.6.18 and
> > 2.6.20-rc3. In both cases kswapd is consuming 10-20% of a CPU and
> > all of the pdflush threads combined (I've seen up to 7 active at
> > once) use maybe 1-2% of cpu time. This occurs regardless of the
> > dirty_ratio setting.
> 
> That sounds a bit much for kswapd. How many nodes? Any cpusets in use?

It's an x86-64 box - an XE 240 - 4 core, 16GB RAM, single node, no cpusets.

> A upper maximum on the number of pdflush threads exists at 8. Are these 
> multiple files or single file transfers?

See the test case i posted - a single file write per filesystem, three
filesystems being written to at once, all on different, unshared block
devices.

Cheers,

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