[linux-pm] [PATCH 0/5] Container Freezer v6: Reuse Suspend Freezer

Vivek Kashyap kashyapv at us.ibm.com
Tue Aug 12 20:47:10 PDT 2008

On Tue, 12 Aug 2008, Andrew Morton wrote:

> On Mon, 11 Aug 2008 16:53:23 -0700
> Matt Helsley <matthltc at us.ibm.com> wrote:
>> This patch series introduces a cgroup subsystem that utilizes the swsusp
>> freezer to freeze a group of tasks. It's immediately useful for batch job
>> management scripts. It should also be useful in the future for implementing
>> container checkpoint/restart.
> I don't think that this provides anything like sufficient detail to justify
> merging a whole bunch of stuff into Linux.
> What does "It's immediately useful for batch job management scripts."
> mean?  How is it useful?  Examples?  Why would an operator want this
> feature, and how would it be used?  _much_ more information is needed!

A batch-manager/job scheduler (such as loadleveler) must at times stop all 
tasks associated with a workload being run in a container. The workload may 
constitute of multiple tasks - some of which are in different sessions. 
A signal (STOP/CONT) to the Containers 'init' wont be transmitted to all 
the tasks in the Container. The 'freezer' mechanism allows this control
to be implemented in a clean way.

> Once we've actually found out what this work is useful for, we can move
> onto identification of and discussion of alternatives.  One would be "why not
> use plain old SIGSTOP?"  Another alternative is, of course "that's not useful
> enough to justify merging the code".  But we don't know yet, coz you didn't
> tell us.
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Vivek Kashyap
Linux Technology Center, IBM

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