On 06/21/2017 05:38 PM, Tejun Heo wrote: > Hello, Waiman. > > On Wed, Jun 14, 2017 at 11:05:35AM -0400, Waiman Long wrote: >> Subtree root mode is a new cgroup mode which applies the following >> restrictions when turned on: >> >> 1) Controllers are only allowed to be passed to the children in >> bypass mode except those with the "enable_on_root" flag on. >> 2) Only 1 child cgroup is allowed. >> >> That lone child can be used as the pseudo root of a container cgroup >> hierarchy. All the resources, if controlled, are in the parent >> cgroup. There will be no control knobs in the child. That makes it >> look and feel like a root. > I'm not sure not having the control files in the child makes that much > difference. It is more a look and feel thing than being useful. The sole purpose is to make the container root looks like a real root as much as possible. >> That pseudo root is also considered to be mixable and so can become >> root of a mixed threaded subtree. The no internal process constraint >> also does not apply. > Heh, you can't just declare a non-root cgroup to be a mixed root but > if you're special casing this and making the kernel play a masquerade > with special node, you can make cgroup provide a mixed root while > hosting the internal processes in a dedicated leaf cgroup which isn't > visible to the nested root, right? That is true. > It's all a game of masquerading tho and doesn't actually enable > anything which isn't possible now. This would definitely be useful > for testing. You are right about that. As mentioned in another email, having bypass mode in subtree_control is useful, I think. The concept of subtree root mode, however, is more toward satisfying PeterZ's idea of container invariant. I won't mind leaving it out if others have no objection to that. Cheers, Longman -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
