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

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Message-ID: <20091031184054.GB1475@ucw.cz>
Date:	Sat, 31 Oct 2009 19:40:54 +0100
From:	Pavel Machek <pavel@....cz>
To:	David Rientjes <rientjes@...gle.com>
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 Tue 2009-10-27 14:12:36, David Rientjes wrote:
> On Tue, 27 Oct 2009, Andrew Morton wrote:
> 
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index dfa4362..7f2aa3e 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -1769,7 +1769,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
> > >  		 * See also cpuset_zone_allowed() comment in kernel/cpuset.c.
> > >  		 */
> > >  		alloc_flags &= ~ALLOC_CPUSET;
> > > -	} else if (unlikely(rt_task(p)))
> > > +	} else if (unlikely(rt_task(p)) && !in_interrupt())
> > >  		alloc_flags |= ALLOC_HARDER;
> > >  
> > >  	if (likely(!(gfp_mask & __GFP_NOMEMALLOC))) {
> > 
> > What are the runtime-observeable effects of this change?
> > 
> 
> 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...

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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