Re: [PATCH v35 1/5] mm: support to get hints of free page blocks

[Wei Wang]

On 07/12/2018 04:13 PM, Michal Hocko wrote:
> On Thu 12-07-18 10:52:08, Wei Wang wrote:
> > On 07/12/2018 10:30 AM, Linus Torvalds wrote:
> > > On Wed, Jul 11, 2018 at 7:17 PM Wei Wang <wei.w.wang@xxxxxxxxx> wrote:
> > > > Would it be better to remove __GFP_THISNODE? We actually want to get all
> > > > the guest free pages (from all the nodes).
> > > Maybe. Or maybe it would be better to have the memory balloon logic be
> > > per-node? Maybe you don't want to remove too much memory from one
> > > node? I think it's one of those "play with it" things.
> > >
> > > I don't think that's the big issue, actually. I think the real issue
> > > is how to react quickly and gracefully to "oops, I'm trying to give
> > > memory away, but now the guest wants it back" while you're in the
> > > middle of trying to create that 2TB list of pages.
> > OK. virtio-balloon has already registered an oom notifier
> > (virtballoon_oom_notify). I plan to add some control there. If oom happens,
> > - stop the page allocation;
> > - immediately give back the allocated pages to mm.
> Please don't. Oom notifier is an absolutely hideous interface which
> should go away sooner or later (I would much rather like the former) so
> do not build a new logic on top of it. I would appreciate if you
> actually remove the notifier much more.
>
> You can give memory back from the standard shrinker interface. If we are
> reaching low reclaim priorities then we are struggling to reclaim memory
> and then you can start returning pages back.

OK. Just curious why oom notifier is thought to be hideous, and has it 
been a consensus?

Best,
Wei