Comment # 14 on bug 1183247 from Michal Koutn���

What I find interesting that libvirtd seems to be probing _its_
libvirtd.service cgroup but it should really be interested in the container
.scope cgroup under machine.slice (to see what's was delegated to the
container) or the root cgroup (to see what is available on the host (for
further delegation)).

The reason might be that other distros enable DefaultMemoryAccounting=yes and
in such a case even libvirtd.service would have memory controller enabled in
itself which is likely enough to trick lxc.