linux-kernel - Re: kswapd craziness in 3.7

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Date:	Sun, 09 Dec 2012 22:59:47 +0100
From:	Zdenek Kabelac <zdenek.kabelac@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Zlatko Calusic <zlatko.calusic@...on.hr>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mgorman@...e.de>, linux-mm <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: kswapd craziness in 3.7

Dne 9.12.2012 02:01, Linus Torvalds napsal(a):
>
>
> On Sat, 8 Dec 2012, Zlatko Calusic wrote:
>>
>> Or sooner... in short: nothing's changed!
>>
>> On a 4GB RAM system, where applications use close to 2GB, kswapd likes to keep
>> around 1GB free (unused), leaving only 1GB for page/buffer cache. If I force
>> bigger page cache by reading a big file and thus use the unused 1GB of RAM,
>> kswapd will soon (in a matter of minutes) evict those (or other) pages out and
>> once again keep unused memory close to 1GB.
>
> Ok, guys, what was the reclaim or kswapd patch during the merge window
> that actually caused all of these insane problems? It seems it was more
> fundamentally buggered than the fifteen-million fixes for kswapd we have
> already picked up.
>
> (Ok, I may be exaggerating the number of patches, but it's starting to
> feel that way - I thought that 3.7 was going to be a calm and easy
> release, but the kswapd issues seem to just keep happening. We've been
> fighting the kswapd changes for a while now.)
>
> Trying to keep a gigabyte free (presumably because that way we have lots
> of high-order alloction pages) is ridiculous. Is it one of the compaction
> changes?
>
> Mel? Ideas?
>

Very true

It's just as simple a making

dd if=/dev/zero of=/tmp/zero bs=1M count=0 seek=1000000

and now

dd if=/tmp/zero of=/dev/null bs=1M

and kswapd fights with dd  for CPU time....


Zdenek


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