linux-kernel - Re: [PATCH 3/3] vmscan: Force kswapd to take notice faster when high-order watermarks are being hit

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Message-Id: <200911040101.50194.elendil@planet.nl>
Date:	Wed, 4 Nov 2009 01:01:46 +0100
From:	Frans Pop <elendil@...net.nl>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, stable@...nel.org,
	linux-kernel@...r.kernel.org,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Sven Geggus <lists@...hsschwanzdomain.de>,
	Karol Lewandowski <karol.k.lewandowski@...il.com>,
	Tobias Oetiker <tobi@...iker.ch>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Rik van Riel <riel@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Stephan von Krawczynski <skraw@...net.com>,
	Kernel Testers List <kernel-testers@...r.kernel.org>
Subject: Re: [PATCH 3/3] vmscan: Force kswapd to take notice faster when high-order watermarks are being hit

On Tuesday 03 November 2009, you wrote:
> > With a representative test I get 0 for kswapd_slept_prematurely.
> > Tested with .32-rc6 + patches 1-3 + this patch.
>
> Assuming the problem actually reproduced, can you still retest with the

Yes, it does.

> patch I posted as a follow-up and see if fast or slow premature sleeps
> are happening and if the problem still occurs please? It's still
> possible with the patch as-is could be timing related. After I posted
> this patch, I continued testing and found I could get counts fairly
> reliably if kswapd was calling printk() before making the premature
> check so the window appears to be very small.

Tested with .32-rc6 and .31.1. With that follow-up patch I still get 
freezes and SKB allocation errors. And I don't get anywhere near the fast, 
smooth and reliable behavior I get when I do the congestion_wait() 
reverts.

The new case does trigger as you can see below, but I'm afraid I don't see 
it making any significant difference for my test. Hope the data is still 
useful for you.

From vmstat for .32-rc6:
kswapd_highorder_rewakeup 8
kswapd_slept_prematurely_fast 329
kswapd_slept_prematurely_slow 55

From vmstat for .31.1:
kswapd_highorder_rewakeup 20
kswapd_slept_prematurely_fast 307
kswapd_slept_prematurely_slow 105

If you'd like me to test with the congestion_wait() revert on top of this 
for comparison, please let me know.

Cheers,
FJP

P.S. Your follow-up patch did not apply cleanly on top of the debug one as 
you seem to have made some changes between posting them (dropped kswapd_ 
from the sleeping_prematurely() function name and added a comment).


View attachment "vmstat.32" of type "text/plain" (1451 bytes)

View attachment "vmstat.31" of type "text/plain" (1376 bytes)