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

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Date:	Sat, 9 May 2009 23:37:38 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	David Rientjes <rientjes@...gle.com>
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 Saturday 09 May 2009, David Rientjes wrote:
> 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,

It doesn't.  All of my allocations are of order 0.

> using the ZONE_OOM_LOCKED approach to locking out the oom killer will work
> just fine in mmotm.

No, it won't, AFAICT.

Best,
Rafael
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