linux-kernel - Re: swapping when there's a free memory

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Date:	Tue, 27 Apr 2010 10:35:17 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Pavel Machek <pavel@....cz>,
	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: swapping when there's a free memory

On Mon, 26 Apr 2010 15:33:33 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Sun, 25 Apr 2010 09:13:49 +0200
> Pavel Machek <pavel@....cz> wrote:
> 
> > Hi!
> > 
> > > I captured this output of vmstat. The machine was freeing cache and 
> > > swapping out pages even when there was a plenty of free memory.
> > > 
> > > The machine is sparc64 with 1GB RAM with 2.6.34-rc4. This abnormal 
> > > swapping happened during running spadfsck --- a fsck program for a custom 
> > > filesystem that caches most reads in its internal cache --- so it reads 
> > > buffers and allocates memory at the same time.
> > > 
> > > Note that sparc64 doesn't have any low/high memory zones, so it couldn't 
> > > be explained by filling one zone and needing to allocate pages in it.
> > 
> > Fragmented memory + high-order allocation?
> 
> Yeah, could be.  I wonder which slab/slub/slob implementation you're
> using, and what page sizes it uses for dentries, inodes, etc.  Can you
> have a poke in /prob/slabinfo?
> 
And please /proc/buddyinfo and /proc/zoneinfo when the system is swappy.

Thanks,
-Kame

> 
> > > This abnormal behavior doesn't happen everytime, it happend about twice 
> > > for many spadfsck attempts.
> > 
> > ...yep, that would be random.
> 
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