Re: [PATCH 1/2] cgroup: implement cgroup_subsys->implicit_on_dfl

From: Tejun Heo
Date: Tue Mar 08 2016 - 10:59:25 EST

On Wed, Feb 24, 2016 at 05:12:54PM -0500, Tejun Heo wrote:
> Some controllers, perf_event for now and possibly freezer in the
> future, don't really make sense to control explicitly through
> "cgroup.subtree_control". For example, the primary role of perf_event
> is identifying the cgroups of tasks; however, because the controller
> also keeps a small amount of state per cgroup, it can't be replaced
> with simple cgroup membership tests.
> This patch implements cgroup_subsys->implicit_on_dfl flag. When set,
> the controller is implicitly enabled on all cgroups on the v2
> hierarchy so that utility type controllers such as perf_event can be
> enabled and function transparently.
> An implicit controller doesn't show up in "cgroup.controllers" or
> "cgroup.subtree_control", is exempt from no internal process rule and
> can be stolen from the default hierarchy even if there are non-root
> csses.
> v2: Reimplemented on top of the recent updates to css handling and
> subsystem rebinding. Rebinding implicit subsystems is now a
> simple matter of exempting it from the busy subsystem check.
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>

Applying this one to cgroup/for-4.6. Waiting for the review of
userland part on the second patch.