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Date: Mon, 18 Nov 2013 17:22:16 -0800 (PST)
From: David Rientjes <rientjes@google.com>
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To: Michal Hocko <mhocko@suse.cz>
cc: Johannes Weiner <hannes@cmpxchg.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
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        cgroups@vger.kernel.org
Subject: Re: [patch 1/2] mm, memcg: avoid oom notification when current needs
 access to memory reserves
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On Mon, 18 Nov 2013, Michal Hocko wrote:

> > Even though the situation may not require a kill, the user still wants
> > to know that the memory hard limit was breached and the isolation
> > broken in order to prevent a kill.  We just came really close and the
> 
> You can observe that you are getting into troubles from fail counter
> already. The usability without more reclaim statistics is a bit
> questionable but you get a rough impression that something is wrong at
> least.
> 

Agreed, but it seems like the appropriate mechanism for this is through 
the memory.{,memsw.}usage_in_bytes notifiers which already exist.

> > fact that current is exiting is coincidental.  Not everybody is having
> > OOM situations on a frequent basis and they might want to know when
> > they are redlining the system and that the same workload might blow up
> > the next time it's run.
> 
> I am just concerned that signaling temporal OOM conditions which do not
> require any OOM killer action (user or kernel space) might be confusing.
> Userspace would have harder times to tell whether any action is required
> or not.
> 

Completely agreed, in fact there is no reliable and non-racy way in 
userspace to determine "is this a real oom condition that I must act upon 
or can the kernel handle it?"