linux-kernel - Re: [PATCH 2/3] page allocator: Do not allow interrupts to use ALLOC

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Message-ID: <alpine.DEB.2.00.0910311248490.13829@chino.kir.corp.google.com>
Date:	Sat, 31 Oct 2009 12:51:14 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Pavel Machek <pavel@....cz>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, stable@...nel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Frans Pop <elendil@...net.nl>, Jiri Kosina <jkosina@...e.cz>,
	Sven Geggus <lists@...hsschwanzdomain.de>,
	Karol Lewandowski <karol.k.lewandowski@...il.com>,
	Tobias Oetiker <tobi@...iker.ch>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Rik van Riel <riel@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Stephan von Krawczynski <skraw@...net.com>,
	kernel-testers@...r.kernel.org
Subject: Re: [PATCH 2/3] page allocator: Do not allow interrupts to use
 ALLOC_HARDER

On Sat, 31 Oct 2009, Pavel Machek wrote:

> > Giving rt tasks access to memory reserves is necessary to reduce latency, 
> > the privilege does not apply to interrupts that subsequently get run on 
> > the same cpu.
> 
> If rt task needs to allocate memory like that, then its broken,
> anyway...
> 

Um, no, it's a matter of the kernel implementation.  We allow such tasks 
to allocate deeper into reserves to avoid the page allocator from 
incurring a significant penalty when direct reclaim is required.  
Background reclaim has already commenced at this point in the slowpath.
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