Re: [RFC] cgroups: freezer -- Allow to attach a task to a frozen cgroup

[Cyrill Gorcunov <gorcunov@gmail.com>]

On Mon, Nov 28, 2011 at 08:08:44AM -0800, Tejun Heo wrote:
> On Mon, Nov 28, 2011 at 04:08:13PM +0400, Cyrill Gorcunov wrote:
> > In checkpoint/restore we need an ability to attach pids to
> > a frozen cgroup. Thus once pid reaches a frozen cgroup it is
> > not rejected, but the task get frozen immediately.
> > 
> > Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
> > ---
> > 
> > I would really appreciate complains and comments.
> 
> First of all, both freezer and cgroup have non-trivial pending
> patchsets (e.g. ->can_attach_task() is scheduled for removal) and I
> have changes which basically try to achieve about the same thing, so
> let's slow down a bit.  I think the problem is a bit more complex.
> 
> Some thoughts I have on cgroup freezer ATM,
> 
...
> 
> * Another improvement that I want to have is allowing cgroup frozen
>   tasks to be killed.  I don't think this matters for system freezer
>   but for cgroup freezer both oom killer and systemd want it.
>

  * Run ptrace over frozen tasks ;)

> So, while I agree with the direction of this patch, I think this
> definitely needs a lot more work to go in.  I don't think we can do
> much until the freezer and cgroup changes are settled.  The freezer
> part is now in Rafael's tree, the cgroup part is going under Linus'
> review.  Once they're complete, I'll provide a merged branch that
> further cgroup works can be based on.
> 

Thanks a lot for comments, Tejun! For own needs I'll make a stub
in our user-space tool, once things are settled down we can move on.