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

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Date:	Sun, 14 Apr 2013 19:39:35 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Serge Hallyn <serge.hallyn@...ntu.com>
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

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.

Thanks.

-- 
tejun
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