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

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Message-ID: <alpine.DEB.2.00.0911021249470.22525@chino.kir.corp.google.com>
Date:	Mon, 2 Nov 2009 12:53:46 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
cc:	Rik van Riel <riel@...hat.com>, Pavel Machek <pavel@....cz>,
	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>,
	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 Mon, 2 Nov 2009, Christoph Lameter wrote:

> What is realtime in this scenario? There are no guarantees that reclaim
> wont have to occur. There are no guarantees anymore and therefore you
> cannot really call this realtime.
> 

Realtime in this scenario is anything with a priority of MAX_RT_PRIO or 
lower.

> Is realtime anything more than: "I want to have my patches merged"?
> 

These allocations are not using ~__GFP_WAIT for a reason, they can block 
on direct reclaim.

But we're convoluting this issue _way_ more than it needs to be.  We have 
used ALLOC_HARDER for these tasks as a convenience for over four years.  
The fix here is to address an omittion in the page allocator refactoring 
code that went into 2.6.31 that dropped the check for !in_interrupt().

If you'd like to raise the concern about the rt exemption being given 
ALLOC_HARDER, then it is seperate from this fix.
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