Re: [PATCH 3/3] cgroup: Implement cgroup2 basic CPU usage accounting

Tejun Heo
2017-08-17T13:14:05Z

Hello,

On Thu, Aug 17, 2017 at 01:07:41PM +0100, Roman Gushchin wrote:
> On Fri, Aug 11, 2017 at 09:37:54AM -0700, Tejun Heo wrote:
> > In cgroup1, while cpuacct isn't actually controlling any resources, it
> > is a separate controller due to combinaton of two factors -
>
> s/combinaton/combination

Fixed.

> > @@ -4466,6 +4470,8 @@ static void css_free_work_fn(struct work_struct *work)
> > */
> > cgroup_put(cgroup_parent(cgrp));
> > kernfs_put(cgrp->kn);
> > + if (cgroup_on_dfl(cgrp))
> > + cgroup_stat_exit(cgrp);
>
> It looks like this "if (cgroup_on_dfl(cgrp))" works here and further similar to
> "#ifdef CGROUP_V2". I wonder, if it's better to move this check into the
> calling function: cgroup_stat_exit() in this case.

I have a slight preference to keeping these topology-aware tests on
the core / management part of code because that makes it obvious that
these stats aren't available for all cgroups. Also, during cgroup
creation, because @cgrp isn't linked to its parent yet, we'd have to
pass @parent to cgroup_stat_init/exit() too.

> > +void cgroup_stat_show_cputime(struct seq_file *seq, const char *prefix)
> > +{
>
> What are any other possible prefix values except "cpu."?

Empty string when the stats are exposed through cpu.stat.

> > +void __init cgroup_stat_boot(void)
> > +{
> > + int cpu;
> > +
> > + for_each_possible_cpu(cpu)
> > + raw_spin_lock_init(per_cpu_ptr(&cgroup_cpu_stat_lock, cpu));
> > +
> > + WARN_ON(cgroup_stat_init(&cgrp_dfl_root.cgrp));
>
> I'm not sure WARN_ON() is enough here: if cgroup_stat_init() returned -ENOMEM,
> the following OOPS is not avoidable, as you don't check cpu_stat pointer.
> But it's very unlikely, of course.

Sure, will switch to BUG_ON().

Thanks.

--
tejun