Commit c43c5ea7 authored Apr 26, 2018 by Tejun Heo

cgroup: Make cgroup_rstat_updated() ready for root cgroup usage



cgroup_rstat_updated() ensures that the cgroup's rstat is linked to
the parent.  If there's no parent, it never gets linked and the
function ends up grabbing and releasing the cgroup_rstat_lock each
time for no reason which can be expensive.

This hasn't been a problem till now because nobody was calling the
function for the root cgroup but rstat is gonna be exposed to
controllers and use cases, so let's get ready.  Make
cgroup_rstat_updated() an no-op for the root cgroup.

Signed-off-by: Tejun Heo <tj@kernel.org>

parent 9a9e97b2

kernel/cgroup/rstat.c

+4 −0

Original line number	Original line	Diff line number	Diff line
	@@ -27,6 +27,10 @@ void cgroup_rstat_updated(struct cgroup *cgrp, int cpu)
	struct cgroup *parent;		struct cgroup *parent;
	unsigned long flags;		unsigned long flags;

			/* nothing to do for root */
			if (!cgroup_parent(cgrp))
			return;

	/*		/*
	* Paired with the one in cgroup_rstat_cpu_pop_upated(). Either we		* Paired with the one in cgroup_rstat_cpu_pop_upated(). Either we
	* see NULL updated_next or they see our updated stat.		* see NULL updated_next or they see our updated stat.