linux-kernel - Re: [patch 1/2] mm, memcg: avoid oom notification when current needs access to memory reserves

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Message-Id: <20140107162503.f751e880410f61a109cdcc2b@linux-foundation.org>
Date:	Tue, 7 Jan 2014 16:25:03 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	David Rientjes <rientjes@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	cgroups@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [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@...e.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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