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

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Message-Id: <1217239487.6331.24.camel@twins>
Date:	Mon, 28 Jul 2008 12:04:47 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alex Samad <alex@...ad.com.au>
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 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.

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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