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

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Message-ID: <20070110230855.GF44411608@melbourne.sgi.com>
Date:	Thu, 11 Jan 2007 10:08:55 +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 03:04:15PM -0800, Christoph Lameter wrote:
> On Thu, 11 Jan 2007, David Chinner wrote:
> 
> > The performance and smoothness is fully restored on 2.6.20-rc3
> > by setting dirty_ratio down to 10 (from the default 40), so
> > something in the VM is not working as well as it used to....
> 
> dirty_background_ratio is left as is at 10?

Yes.

> So you gain performance by switching off background writes via pdflush?

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.

Cheers,

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