linux-kernel - Re: kswapd craziness in 3.7

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Date:	Mon, 03 Dec 2012 09:30:12 +0100
From:	Thorsten Leemhuis <fedora@...mhuis.info>
To:	Johannes Weiner <hannes@...xchg.org>
CC:	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	George Spelvin <linux@...izon.com>,
	Johannes Hirte <johannes.hirte@....tu-ilmenau.de>,
	Tomas Racek <tracek@...hat.com>, Jan Kara <jack@...e.cz>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Josh Boyer <jwboyer@...il.com>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Jiri Slaby <jslaby@...e.cz>,
	Zdenek Kabelac <zkabelac@...hat.com>,
	Bruno Wolff III <bruno@...ff.to>,
	linux-mm <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	John Ellson <john.ellson@...cast.net>
Subject: Re: kswapd craziness in 3.7

Hi!

Johannes Weiner wrote on 01.12.2012 01:45:
> On Fri, Nov 30, 2012 at 01:39:03PM +0100, Thorsten Leemhuis wrote:
>> /me wonders how to elegantly get out of his man-in-the-middle position
> You control the mighty koji :-)

Something even a journalist can ;-)

> But seriously, this is very helpful, thank you!

Np; BTW, in case anybody here on LKML cares: I started maintaining a
side repo (PPA in ubuntu speak) a few weeks ago that offers kernel
vanilla builds (mainline and stable) for the Fedora 17 and 18; see
https://fedoraproject.org/wiki/Kernel_Vanilla_Repositories
for details. It's not as good and up2date yet as I would like it, but
one has to start somewhere.

Back to topic:

> John now also Cc'd directly.
> 
>> John was able to reproduce the problem quickly with a kernel that 
>> contained the patch from your mail. For details see
>
> [stripped: all the glory details of what likely went wrong and lead
> to the problem john sees or saw]
>
> ---
> From: Johannes Weiner <hannes@...xchg.org>
> Subject: [patch] mm: vmscan: do not keep kswapd looping forever due
>  to individual uncompactable zones
> 
> When a zone meets its high watermark and is compactable in case of
> higher order allocations, it contributes to the percentage of the
> node's memory that is considered balanced.
> [...]

FYI: I built a kernel with that patch. I've been running on my x86_64
machine at home over the weekend and everything was working fine (just
as without the patch). John gave it a quick try and in
https://bugzilla.redhat.com/show_bug.cgi?id=866988#c57 reported:

"""
I just installed
kernel-3.7.0-0.rc7.git1.2.van.main.knurd.kswap.4.fc18.i686 and ran my
usual load that triggers the problem.  OK so far.  I'll check again in
24hours, but looking good so far.
"""

BTW, I built that kernel without the patch you mentioned in
http://thread.gmane.org/gmane.linux.kernel.mm/90911/focus=91153
("buffer_heads_over_limit can put kswapd into reclaim, but it's ignored
[...]) It looked to me like that patch was only meant for debugging. Let
me know if that was wrong. Ohh, and I didn't update to a fresher
mainline checkout yet to make sure the base for John's testing didn't
change.

CU
 Thorsten
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