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

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

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?"
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