linux-kernel - Re: [patch 2/2] mm: memcontrol: default hierarchy interface for memory

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Message-ID: <20150114160101.GA30018@phnom.home.cmpxchg.org>
Date:	Wed, 14 Jan 2015 11:01:01 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Greg Thelen <gthelen@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	Vladimir Davydov <vdavydov@...allels.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 2/2] mm: memcontrol: default hierarchy interface for
 memory

On Tue, Jan 13, 2015 at 03:20:08PM -0800, Greg Thelen wrote:
> 
> On Thu, Jan 08 2015, Johannes Weiner wrote:
> 
> > Introduce the basic control files to account, partition, and limit
> > memory using cgroups in default hierarchy mode.
> >
> > This interface versioning allows us to address fundamental design
> > issues in the existing memory cgroup interface, further explained
> > below.  The old interface will be maintained indefinitely, but a
> > clearer model and improved workload performance should encourage
> > existing users to switch over to the new one eventually.
> >
> > The control files are thus:
> >
> >   - memory.current shows the current consumption of the cgroup and its
> >     descendants, in bytes.
> >
> >   - memory.low configures the lower end of the cgroup's expected
> >     memory consumption range.  The kernel considers memory below that
> >     boundary to be a reserve - the minimum that the workload needs in
> >     order to make forward progress - and generally avoids reclaiming
> >     it, unless there is an imminent risk of entering an OOM situation.
> 
> So this is try-hard, but no-promises interface.  No complaints.  But I
> assume that an eventual extension is a more rigid memory.min which
> specifies a minimum working set under which an container would prefer an
> oom kill to thrashing.

Yes, memory.min would nicely complement memory.max and I wouldn't be
opposed to adding it.  However, that does require at least some level
of cgroup-awareness in the global OOM killer in order to route kills
meaningfully according to cgroup configuration, which is mainly why I
deferred it in this patch.
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