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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>
This commit is contained in:
Tejun Heo 2018-04-26 14:29:06 -07:00
parent 9a9e97b2f1
commit c43c5ea75f
1 changed files with 4 additions and 0 deletions
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4
kernel/cgroup/rstat.c
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@ -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.