Comment # 7 on bug 1222450 from Franck Bui

(In reply to Aleksa Sarai from comment #5)
> So, the issue is that systemd is not enabling all of the controllers at the
> root (subtree_control is missing a bunch of controllers on your system),

AFAIK the controllers are usually enabled on demand, ie if no unit requires
them then they remain disabled.

It's actually important because usually (some) cgroup controllers incur some
performance penalties to the whole system even if only one single unit needs
them.

That's for this reasons that it was requested to leave most of the controllers
disabled by default:

--- %< ---
# rpm -q --changelog systemd-default-settings | head -n7
* Wed Apr 10 2024 Franck Bui <fbui@suse.com>
- Import 0.10
  5088997 SLE: Disable pids controller limit under user instances
(jsc#SLE-10123)

* Thu Mar 28 2024 Franck Bui <fbui@suse.com>
- Import 0.9
  bb859bf user@.service: Disable controllers by default (jsc#PED-2276)
--- >% ----