linux-kernel - Re: [PATCH 4/4] memcg: force use_hierarchy if sane

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Date:	Mon, 15 Apr 2013 00:29:24 -0500
From:	Serge Hallyn <serge.hallyn@...ntu.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	lizefan@...wei.com, containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, mhocko@...e.cz, vgoyal@...hat.com,
	cgroups@...r.kernel.org
Subject: Re: [PATCH 4/4] memcg: force use_hierarchy if sane_behavior

Quoting Tejun Heo (tj@...nel.org):
> Hello, Serge.
> 
> On Sun, Apr 14, 2013 at 08:13:36PM -0500, Serge Hallyn wrote:
> > If I do
> > 
> > 	cd /sys/fs/cgroup/memory
> > 	mkdir b
> > 	cd b
> > 	echo 1 > memory.use_hierarchy
> > 	echo 5000 > memory.limit_in_bytes
> > 	cat memory.limit_in_bytes
> > 8192
> > 	mkdir c
> > 	cd c
> > 	cat memory.use_hierarchy
> > 1
> > 	cat memory.limit_in_bytes
> > 9223372036854775807
> > 	echo $$ > tasks
> > 	bash
> > <killed>
> > 
> > So it seems the hierarchy is being enforced, but not reported in
> > child limit_in_bytes files.
> 
> Hmm.... if I understand you correctly, it ain't bug.  It's supposed to
> work that way.  The parent has certain limits and the child doesn't.
> The child will operate within the paren't limits but in those limits
> it isn't restricted.  We actually have a controller which does
> propagate configuration, the device security one, which I don't think
> is really optimal but it seems to be the easier way to implement
> hierarchical behavior for that controller.
> 
> Anyways, if you think about the use cases, the current memcg way makes
> a lot more sense and is more flexible.  e.g. You can express things
> like A + B shouldn't go above 1000 (whatever the unit is) but A and B
> in each can go upto 700 when there's room.

True, that makes sense, thanks.

This example would be great to have in Documentation/cgroups/memory.txt.
Perhaps as a new subsection 6.2?

-serge
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