linux-kernel - Re: [PATCH 1/5] mm: Add __GFP_NO_OOM

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Message-ID: <alpine.DEB.2.00.0905091415310.1124@chino.kir.corp.google.com>
Date:	Sat, 9 May 2009 14:22:48 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Andrew Morton <akpm@...ux-foundation.org>, fengguang.wu@...el.com,
	linux-pm@...ts.linux-foundation.org, pavel@....cz,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	jens.axboe@...cle.com, alan-jenkins@...fmail.co.uk,
	linux-kernel@...r.kernel.org, kernel-testers@...r.kernel.org,
	Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH 1/5] mm: Add __GFP_NO_OOM_KILL flag

On Sat, 9 May 2009, Rafael J. Wysocki wrote:

> > All of your tasks are in D state other than kthreads, right?  That means 
> > they won't be in the oom killer (thus no zones are oom locked), so you can 
> > easily do this
> > 
> > 	struct zone *z;
> > 	for_each_populated_zone(z)
> > 		zone_set_flag(z, ZONE_OOM_LOCKED);
> > 
> > and then
> > 
> > 	for_each_populated_zone(z)
> > 		zone_clear_flag(z, ZONE_OOM_LOCKED);
> > 
> > The serialization is done with trylocks so this will never invoke the oom 
> > killer because all zones in the allocator's zonelist will be oom locked.
> 
> Well, that might have been a good idea if it actually had worked. :-(
> 
> > Why does this not work for you?
> 
> If I set image_size to something below "hard core working set" +
> totalreserve_pages, preallocate_image_memory() hangs the
> box (please refer to the last patch I sent,
> http://patchwork.kernel.org/patch/22423/).
> 

This has been changed in the latest mmotm with Mel's page alloactor 
patches (and I think yours should be based on mmotm).  Specifically, 
page-allocator-break-up-the-allocator-entry-point-into-fast-and-slow-paths.patch.

Before his patchset, zonelists that had ZONE_OOM_LOCKED set for at least 
one of their zones would unconditionally goto restart.  Now, if
order > PAGE_ALLOC_COSTLY_ORDER, it gives up and returns NULL.  Otherwise, 
it does goto restart.

So if your allocation has order > PAGE_ALLOC_COSTLY_ORDER, using the 
ZONE_OOM_LOCKED approach to locking out the oom killer will work just fine 
in mmotm.
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