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

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Message-ID: <20170817120741.GA22854@castle.DHCP.thefacebook.com>
Date:   Thu, 17 Aug 2017 13:07:41 +0100
From:   Roman Gushchin <guro@...com>
To:     Tejun Heo <tj@...nel.org>
CC:     <lizefan@...wei.com>, <hannes@...xchg.org>, <peterz@...radead.org>,
        <mingo@...hat.com>, <longman@...hat.com>,
        <cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kernel-team@...com>, <pjt@...gle.com>, <luto@...capital.net>,
        <efault@....de>, <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 3/3] cgroup: Implement cgroup2 basic CPU usage accounting

Hi Tejun!

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

> @@ -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.


> +void cgroup_stat_show_cputime(struct seq_file *seq, const char *prefix)
> +{

What are any other possible prefix values except "cpu."?

> +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.


Overall looks very good!

Thanks!