Possibly related (same subject, not in this thread)

• 2015-02-11 · Re: [PATCHv3 8/8] cgroup: Add documentation for cgroup namespaces · Tejun Heo <tj@kernel.org>
• 2015-02-11 · Re: [PATCHv3 8/8] cgroup: Add documentation for cgroup namespaces · Eric W. Biederman <hidden>
• 2015-02-11 · Re: [PATCHv3 8/8] cgroup: Add documentation for cgroup namespaces · Tejun Heo <tj@kernel.org>
• 2015-02-11 · Re: [PATCHv3 8/8] cgroup: Add documentation for cgroup namespaces · "Serge E. Hallyn" <serge@hallyn.com>
• 2015-02-11 · Re: [PATCHv3 8/8] cgroup: Add documentation for cgroup namespaces · Tejun Heo <tj@kernel.org>

A slightly off topic comment, for where this thread has gone but
relevant if we are talking about cgroup namespaces.

If don't implement compatibility with existing userspace, they get a
nack.  A backwards-incompatible change should figure out how to remove
the need for any namespaces.

Because that is what namespaces are about backwards compatibility.

Eric