Re: [PATCH 1/5] mm: Add __GFP_NO_OOM_KILL flag

David Rientjes
2009-05-09T21:22:48Z

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.