From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Rientjes <rientjes-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH 1/5] mm: Add __GFP_NO_OOM_KILL flag
Date: Sat, 9 May 2009 14:22:48 -0700 (PDT)
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To: "Rafael J. Wysocki" <rjw-KKrjLPT3xs0@public.gmane.org>
Cc: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, fengguang.wu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, linux-pm-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, pavel-+ZI9xUNit7I@public.gmane.org, Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, jens.axboe-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org, alan-jenkins-cCz0Lq7MMjm9FHfhHBbuYA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kernel-testers-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Mel Gorman <mel-wPRd99KPJ+uzQB+pC5nmwQ@public.gmane.org>

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.