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

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:

quoted

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.

quoted

@@ -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.

quoted

+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.

quoted

+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