[Pkg-systemd-maintainers] Bug#732584: Want documentation for cgroup persistence implications

[Uoti Urpala]

This setting was removed in systemd v205 as a part of the control group
rework. Improving documentation of what it did in v204 is likely not
worth the effort.

My guess is that it did not have effects like "result in all descendants
of the main service daemon to be killed", but only mattered if you did
(now deprecated) direct access to the cgroup tree.