linux-kernel - Re: [Bug #14141] order 2 page allocation failures in iwlagn

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Date:	Wed, 14 Oct 2009 17:50:52 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	reinette chatre <reinette.chatre@...el.com>
Cc:	Frans Pop <elendil@...net.nl>,
	David Rientjes <rientjes@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Karol Lewandowski <karol.k.lewandowski@...il.com>,
	"Abbas, Mohamed" <mohamed.abbas@...el.com>,
	"John W. Linville" <linville@...driver.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [Bug #14141] order 2 page allocation failures in iwlagn

On Wed, Oct 14, 2009 at 09:28:00AM -0700, reinette chatre wrote:
> Hi Mel,
> 
> On Wed, 2009-10-14 at 03:30 -0700, Mel Gorman wrote:
> > From 5fb9f897117bf2701f9fdebe4d008dbe34358ab9 Mon Sep 17 00:00:00 2001
> > From: Mel Gorman <mel@....ul.ie>
> > Date: Wed, 14 Oct 2009 11:19:57 +0100
> > Subject: [PATCH] iwlwifi: Suppress warnings related to GFP_ATOMIC allocations that do not matter
> > 
> > iwlwifi refills RX buffers in two ways - a direct method using GFP_ATOMIC
> > and a tasklet method using GFP_KERNEL. There are a number of RX buffers and
> > there are only serious issues when there are no RX buffers left. The driver
> > explicitly warns when refills are failing and the buffers are low but it
> > always warns when a GFP_ATOMIC allocation fails even when there is no
> > packet loss as a result.
> 
> 
> No, it does not always warn when a GFP_ATOMIC allocation fails. Please
> check earlier in iwl_rx_allocate() we have:
> 
> if (rxq->free_count > RX_LOW_WATERMARK)
> 	priority |= __GFP_NOWARN;
> 
> So it will suppress warnings as long as we have buffers available.
> 
> We do want to see warnings if memory is below watermark and allocation
> fails - your patch prevents these warnings from appearing.
> 

Yeah, the patch is balls and is not the way forward.

What is your take on GFP_ATOMIC-direct deleting the pool before the tasklet
can refill it with GFP_KERNEL? Should direct allocation be falling back to
calling with GFP_KERNEL when the pool has been depleted instead of failing?



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