linux-kernel - Re: [PATCH] control groups: documentation improvements

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Message-ID: <531DC971.6020208@gopivotal.com>
Date:	Mon, 10 Mar 2014 14:17:21 +0000
From:	Glyn Normington <gnormington@...ivotal.com>
To:	Tejun Heo <tj@...nel.org>
CC:	linux-kernel@...r.kernel.org, Li Zefan <lizefan@...wei.com>
Subject: Re: [PATCH] control groups: documentation improvements

Hi Tejun

Thanks for your quick reply. Responses inline.

Regards,
Glyn

On 10/03/2014 14:07, Tejun Heo wrote:
> Hello, Glyn.
>
> On Mon, Mar 10, 2014 at 11:39:28AM +0000, Glyn Normington wrote:
>> Clarify that each hierarchy must be associated with at least one
>> subsystem.
> Hmmm... but named hierarchies can exist without any controllers
> attached to them.
Then we missed how to create a hierarchy with no associated subsystems. 
The only way I can think of is to use mount, specify no subsystems on -o 
(which defaults to all the subsystems defined in the kernel), and run it 
in a kernel with no subsystems defined (which seems unlikely these days).

Is that what you had in mind or is there some other way of creating a 
hierarchy with no subsystems attached?
>
>> Clarify that subsystems may be attached to multiple hierarchies,
>> although this isn't very useful, and explain what happens.
> And a subsystem may only be attached to a single hierarchy.
Perhaps that's what should happen, but the following experiment 
demonstrates a subsystem being attached to two hierarchies:

$ pwd
/home/vagrant
$ mkdir mem1
$ mkdir mem2
$ sudo su
# mount -t cgroup -o memory none /home/vagrant/mem1
# mount -t cgroup -o memory none /home/vagrant/mem2
# cd mem1
# mkdir inst1
# ls inst1
cgroup.clone_children  memory.failcnt ...
# ls ../mem2
cgroup.clone_children  inst1 memory.limit_in_bytes ...
# cd inst1
# echo 1000000 > memory.limit_in_bytes
# cat memory.limit_in_bytes
1003520
# cat ../../mem2/inst1/memory.limit_in_bytes
1003520
# echo $$ > tasks
# cat tasks
1365
1409
# cat ../../mem2/inst1/tasks
1365
1411
>
> Thanks.
>

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