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

Rafael J. Wysocki
2009-05-09T21:37:38Z

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