Pull cgroup updates from Tejun Heo:

 - cgroup.kill is added which implements atomic killing of the whole
   subtree.

   Down the line, this should be able to replace the multiple userland
   implementations of "keep killing till empty".

 - PSI can now be turned off at boot time to avoid overhead for
   configurations which don't care about PSI.

* 'for-5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: make per-cgroup pressure stall tracking configurable
  cgroup: Fix kernel-doc
  cgroup: inline cgroup_task_freeze()
  tests/cgroup: test cgroup.kill
  tests/cgroup: move cg_wait_for(), cg_prepare_for_wait()
  tests/cgroup: use cgroup.kill in cg_killall()
  docs/cgroup: add entry for cgroup.kill
  cgroup: introduce cgroup.kill