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

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Message-Id: <20100426153333.93c03e98.akpm@linux-foundation.org>
Date:	Mon, 26 Apr 2010 15:33:33 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Pavel Machek <pavel@....cz>
Cc:	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 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?


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

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