linux-kernel - Re: page swap allocation error/failure in 2.6.25

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Message-ID: <20080729000618.GE1747@samad.com.au>
Date:	Tue, 29 Jul 2008 10:06:18 +1000
From:	Alex Samad <alex@...ad.com.au>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm <linux-mm@...ck.org>,
	Mel Gorman <mel@...net.ie>
Subject: Re: page swap allocation error/failure in 2.6.25

On Mon, Jul 28, 2008 at 12:04:47PM +0200, Peter Zijlstra wrote:
> On Sun, 2008-07-27 at 16:07 +1000, Alex Samad wrote:
> > On Fri, Jul 25, 2008 at 09:40:01AM +0200, Peter Zijlstra wrote:
> > > On Fri, 2008-07-25 at 17:20 +1000, Alex Samad wrote:
> > > > Hi
> > 
> > [snip]
> > 
> > > 
> > > 
> > > Its harmless if it happens sporadically. 
> > > 
> > > Atomic order 2 allocations are just bound to go wrong under pressure.
> > can you point me to any doco that explains this ?
> 
> An order 2 allocation means allocating 1<<2 or 4 physically contiguous
> pages. Atomic allocation means not being able to sleep.
> 
> Now if the free page lists don't have any order 2 pages available due to
> fragmentation there is currently nothing we can do about it.

Strange cause I don't normal have a high swap usage, I have 2G ram and
2G swap space. There is not that much memory being used squid, apache is
about it.

> 
> I've been meaning to try and play with 'atomic' page migration to try
> and assemble a higher order page on demand with something like memory
> compaction.
> 
> But its never managed to get high enough on the todo list..
> 
> 

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