Misunderstanding documentation on enabling cgroup controllers

[Nicky Chorley]

Hi folks,

The documentation for enabling and disabling cgroup controllers at
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/admin-guide/cgroup-v2.rst#n403
says that no controllers are enabled by default and to enable them,
one needs to write into cgroup.subtree_control.

I thought this meant that if I didn't enable a controller, I couldn't
control those resources. However, I wrote a program to limit the
number of processes in a cgroup and it works as expected - if I try to
create more processes, I'm unable to. I didn't write "+pids" into
cgroup.subtree_control - that file remains empty.

Am I misunderstanding the documentation, then?

Thanks.