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

Rafael J. Wysocki
2009-05-07T18:09:52Z

On Wednesday 06 May 2009, Andrew Morton wrote:
> On Wed, 6 May 2009 01:20:34 +0200
> "Rafael J. Wysocki" <rjw-KKrjLPT3xs0@public.gmane.org> wrote:
>
> > On Wednesday 06 May 2009, Andrew Morton wrote:
> > > On Wed, 6 May 2009 00:19:35 +0200
> > > "Rafael J. Wysocki" <rjw-KKrjLPT3xs0@public.gmane.org> wrote:
> > >
> > > > > > + && !processes_are_frozen()) {
> > > > > > if (!try_set_zone_oom(zonelist, gfp_mask)) {
> > > > > > schedule_timeout_uninterruptible(1);
> > > > > > goto restart;
> > > > >
> > > > > Cool, that looks like the semantics of __GFP_NO_OOM_KILL without requiring
> > > > > a new gfp flag. Thanks.
> > > >
> > > > Well, you're welcome.
> > > >
> > > > BTW, I think that Andrew was actually right when he asked if I checked whether
> > > > the existing __GFP_NORETRY would work as-is for __GFP_FS set and
> > > > __GFP_NORETRY unset. Namely, in that case we never reach the code before
> > > > nopage: that checks __GFP_NORETRY, do we?
> > > >
> > > > So I think we shouldn't modify the 'else if' condition above and check for
> > > > !processes_are_frozen() at the beginning of the block below.
> > >
> > > Confused.
> > >
> > > I'm suspecting that hibernation can allocate its pages with
> > > __GFP_FS|__GFP_WAIT|__GFP_NORETRY|__GFP_NOWARN, and the page allocator
> > > will dtrt: no oom-killings.
> > >
> > > In which case, processes_are_frozen() is not needed at all?
> >
> > __GFP_NORETRY alone causes it to fail relatively quickly, but I'll try with
> > the combination.
>
> OK. __GFP_WAIT is the big hammer.

Unfortunately it fails too quickly with the combination as well, so it looks
like we can't use __GFP_NORETRY during hibernation.