linux-kernel - Re: iwlagn: order 2 page allocation failures

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Message-ID: <20090911084717.GB32497@csn.ul.ie>
Date:	Fri, 11 Sep 2009 09:47:17 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	reinette chatre <reinette.chatre@...el.com>
Cc:	Frans Pop <elendil@...net.nl>,
	Larry Finger <Larry.Finger@...inger.net>,
	"John W. Linville" <linville@...driver.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"ipw3945-devel@...ts.sourceforge.net" 
	<ipw3945-devel@...ts.sourceforge.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"cl@...ux-foundation.org" <cl@...ux-foundation.org>,
	"Krauss, Assaf" <assaf.krauss@...el.com>,
	Johannes Berg <johannes@...solutions.net>,
	"Abbas, Mohamed" <mohamed.abbas@...el.com>
Subject: Re: iwlagn: order 2 page allocation failures

On Thu, Sep 10, 2009 at 02:14:50PM -0700, reinette chatre wrote:
> On Thu, 2009-09-10 at 02:02 -0700, Mel Gorman wrote:
> 
> > 
> > As a total aside, there is still the problem that the driver is depending on
> > order-2 allocations. On systems without swap, the allocation problem could be
> > more severe as there are fewer pages the system can use to regain contiguity.
> 
> I looked more at the implementation and hardware interface but I do not
> see a way around this. We have to provide 8k buffer to device, and we
> have to make sure it is aligned. 
> 

That would imply an order-1 allocation instead of an order-2 though so
it would appear than we are being worse than we have to. It would appear
to be because of this +256 bytes that goes onto every buffer.

> Do you have any suggestions?
> 

Nothing concrete. Finding an alternative to having the socket buffer
8192+256 to make it an order-1 allocation would be an improvement but I
don't know how that should be tackled. Lacking the hardware, I can't
experiment myself :(

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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