linux-kernel - Re: [RFC PATCH v2] cgroup: Track time in cgroup v2 freezer

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Message-ID: <dbx8jz3zamk2.fsf@ynaffit-andsys.c.googlers.com>
Date: Tue, 22 Jul 2025 15:27:25 -0700
From: Tiffany Yang <ynaffit@...gle.com>
To: Chen Ridong <chenridong@...weicloud.com>
Cc: "Michal Koutný" <mkoutny@...e.com>, linux-kernel@...r.kernel.org, 
	John Stultz <jstultz@...gle.com>, Thomas Gleixner <tglx@...utronix.de>, Stephen Boyd <sboyd@...nel.org>, 
	Anna-Maria Behnsen <anna-maria@...utronix.de>, Frederic Weisbecker <frederic@...nel.org>, 
	Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Pavel Machek <pavel@...nel.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Chen Ridong <chenridong@...wei.com>, 
	kernel-team@...roid.com, Jonathan Corbet <corbet@....net>, cgroups@...r.kernel.org, 
	linux-doc@...r.kernel.org
Subject: Re: [RFC PATCH v2] cgroup: Track time in cgroup v2 freezer

Hi Rindong,

Chen Ridong <chenridong@...weicloud.com> writes:

> On 2025/7/17 20:56, Michal Koutný wrote:
>> Hello Tiffany.

>> On Sun, Jul 13, 2025 at 10:00:09PM -0700, Tiffany Yang  
>> <ynaffit@...gle.com> wrote:

>>> --- a/Documentation/admin-guide/cgroup-v2.rst
>>> +++ b/Documentation/admin-guide/cgroup-v2.rst
>>> @@ -1018,6 +1018,14 @@ All cgroup core files are prefixed with "cgroup."
>>>   	it's possible to delete a frozen (and empty) cgroup, as well as
>>>   	create new sub-cgroups.

>>> +  cgroup.freeze.stat

>> With the given implementation (and use scenario), this'd better exposed
>> in
>>    cgroup.freeze.stat.local


> Would it be possible to add this field to either cgroup.event or  
> cgroup.stat?
> Since the frozen status is already tracked in cgroup.event, this  
> placement would maintain better
> cohesion with existing metrics.

> This is just a suggestion.

> Best regards,
> Ridong

Thanks for taking a look!

I don't think this would *quite* fit in cgroup.event because we're
measuring when the cgroup begins freezing instead of when it reaches the
frozen state. I also worry that having the value so close to
cgroup.frozen would cause additional confusion about its
meaning. cgroup.stat seems reasonable, but the values inside appear to
be accounted for hierarchically, which wouldn't suit our use case.

-- 
Tiffany Y. Yang