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

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Message-ID: <45A57333.6060904@yahoo.com.au>
Date:	Thu, 11 Jan 2007 10:13:55 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	David Chinner <dgc@....com>
CC:	Christoph Lameter <clameter@....com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [REGRESSION] 2.6.19/2.6.20-rc3 buffered write slowdown

David Chinner wrote:
> 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.

Hi David,

Could you get /proc/vmstat deltas for each kernel, to start with?

I'm guessing CPU time isn't a problem, but if it is then I guess
profiles as well.

Thanks,
Nick

-- 
SUSE Labs, Novell Inc.
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