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

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Message-ID: <20130415011336.GF8408@sergelap>
Date:	Sun, 14 Apr 2013 20:13:36 -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):
> Turn on use_hierarchy by default if sane_behavior is specified and
> don't create .use_hierarchy file.
> 
> It is debatable whether to remove .use_hierarchy file or make it ro as
> the former could make transition easier in certain cases; however, the
> behavior changes which will be gated by sane_behavior are intensive
> including changing basic meaning of certain control knobs in a few
> controllers and I don't really think keeping this piece would make
> things easier in any noticeable way, so let's remove it.

Hi Tejun,

this actually reminds me of something that's been on my todo list to
report for some time, but I haven't had time to find the source of the
bug...  And maybe it's already been reported...  but

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.

(Last tested tonight on 3.8.0-17-generic #27-Ubuntu fwiw)

-serge
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