On Mon, Jul 29, 2013 at 10:03:35AM -0700, Eric W. Biederman wrote:

Yes.  From the looks of the looks of it the cgroup implementation is
rather badly borked right now, and definitely not up to the standards of
the other core pieces of the kernel.  One of the reasons I was rather
apalled when systemd started using them.  Until the code actually works
reliably and the races are removed most people's systems would be much
better off with cgroups compiled out.

A single unified hierarchy is a really nasty idea for the same set of
reasons. You have to recompile to disable a controller to see if it that
controller's bugs are what are causing problems on your production
system.  Compiles or even just a reboot is a very heavy hammer to ask
people to use when they are triaging a problem.

That's not how it works.  You can always select which controllers you
want to mount during runtime.  Unified hierarchy only means that there
is one cgroup tree for all mounted controllers, rather than every
controller having its own separate cgroup tree.

If you are like most users and currently mount all controllers in the
same directory so that their cgroup trees overlap and appear to be a
single tree, nothing changes for you.