Re: [PATCH v6] memcg: event control at vmpressure.

From: Michal Hocko <mhocko@suse.cz>
To: Minchan Kim <minchan@kernel.org>
Cc: Hyunhee Kim <hyunhee.kim@samsung.com>,
	'Anton Vorontsov' <anton@enomsg.org>,
	linux-mm@kvack.org, akpm@linux-foundation.org, rob@landley.net,
	kamezawa.hiroyu@jp.fujitsu.com, hannes@cmpxchg.org,
	rientjes@google.com, kirill@shutemov.name,
	'Kyungmin Park' <kyungmin.park@samsung.com>
Subject: Re: [PATCH v6] memcg: event control at vmpressure.
Date: Tue, 25 Jun 2013 18:07:56 +0200	[thread overview]
Message-ID: <20130625160756.GB10617@dhcp22.suse.cz> (raw)
In-Reply-To: <20130621162743.GA2837@gmail.com>

Hi,

On Sat 22-06-13 01:27:43, Minchan Kim wrote:
> > > Question.
> > > 
> > > 1. user: set critical edge
> > > 2. kernel: memory is tight and trigger event with critical
> > > 3. user: kill a program when he receives a event
> > > 4. kernel: memory is very tight again and want to trigger a event
> > >    with critical but fail because last_level was critical and it was edge.
> > > 
> > > Right?
> > 
> > yes, this is the risk of the edge triggering and the user has to be
> > prepared for that. I still think that it makes some sense to have the
> > two modes.
> 
> I'm not sure it's good idea.
> How could user overcome above problem?

Well, if the interface is proposed to workaround issues of the current
implementation then it is surely not a good path. 

I was referring to a concept of edge triggering which makes some sense
to me.  Consider one shot actions that should start/stop a certain
action when the level changes (e.g. very popular notification to admin).

[...]
-- 
Michal Hocko
SUSE Labs

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