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SubjectRe: [patch 1/2] mm, memcg: avoid oom notification when current needs access to memory reserves
On Thu, 19 Dec 2013 15:41:34 +0100 Michal Hocko <mhocko@suse.cz> wrote:

> On Wed 18-12-13 22:09:12, David Rientjes wrote:
> > On Wed, 18 Dec 2013, Michal Hocko wrote:
> >
> > > > For memory isolation, we'd only want to bypass memcg charges when
> > > > absolutely necessary and it seems like TIF_MEMDIE is the only case where
> > > > that's required. We don't give processes with pending SIGKILLs or those
> > > > in the exit() path access to memory reserves in the page allocator without
> > > > first determining that reclaim can't make any progress for the same reason
> > > > and then we only do so by setting TIF_MEMDIE when calling the oom killer.
> > >
> > > While I do understand arguments about isolation I would also like to be
> > > practical here. How many charges are we talking about? Dozen pages? Much
> > > more?
> >
> > The PF_EXITING bypass is indeed much less concerning than the
> > fatal_signal_pending() bypass.

I just spent a happy half hour reliving this thread and ended up
deciding I agreed with everyone! I appears that many more emails are
needed so I think I'll drop
http://ozlabs.org/~akpm/mmots/broken-out/mm-memcg-avoid-oom-notification-when-current-needs-access-to-memory-reserves.patch
for now.

The claim that
mm-memcg-avoid-oom-notification-when-current-needs-access-to-memory-reserves.patch
will impact existing userspace seems a bit dubious to me.

> OK, so can we at least agree on the patch posted here:
> https://lkml.org/lkml/2013/12/12/129. This is a real bug and definitely
> worth fixing.

Yes, can we please get Eric's bug fixed? I don't believe that Eric has
tested either https://lkml.org/lkml/2013/12/12/129 or
http://ozlabs.org/~akpm/mmots/broken-out/mm-memcg-avoid-oom-notification-when-current-needs-access-to-memory-reserves.patch.
Is he the only person who can reproduce this?



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