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

Rafael J. Wysocki
2009-05-08T23:55:43Z

On Thursday 07 May 2009, David Rientjes wrote:
> On Thu, 7 May 2009, Rafael J. Wysocki wrote:
>
> > OK, let's try with __GFP_NO_OOM_KILL first. If there's too much disagreement,
> > I'll use the freezer-based approach instead.
> >
>
> Third time I'm going to suggest this, and I'd like a response on why it's
> not possible instead of being ignored.
>
> 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/).

However, with the freezer-based disabling of the OOM killer it doesn't hang
under the same test conditions.

The difference appears to be that using your approach makes
__alloc_pages_internal() loop forever between the !try_set_zone_oom() test and
restart:, while it should go to nopage: in that situation.

So, I think I'll stick to the Andrew's approach with using __GFP_NO_OOM_KILL.

Thanks,
Rafael