Re: [PATCHv3 8/8] cgroup: Add documentation for cgroup namespaces

From: Tejun Heo
Date: Wed Feb 11 2015 - 11:04:05 EST

On Wed, Feb 11, 2015 at 05:00:23PM +0100, Serge E. Hallyn wrote:
> We absolutely would love to use cgroup namespaces to run older
> userspace in containers. I don't know that it's actually possible
> to do both that and use unified hierarchy at the same time though,
> which is unfortunate. So an Ubuntu 12.04 container will never, afaics,
> be able to run inside an ubuntu 16.04 host that is using unified
> hierarchy, without using backported newer versions of lxc (etc) in
> the container.

So, the constraint there are the controllers. A controller can't be
attached to two hierarchies at the same time for obvious reasons, so
regardless of NS, you can't use the same controller on a unified
hierarchy *and* a traditional hierarchy. NS doesn't adds or
substracts from the situation. If you decide to attach a controller
to a traditional hierarchy, that's where it's gonna be available. If
you attach it to the unified hierarchy, the same story.


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