linux-kernel - Re: [PATCH v4 0/2] cgroup: Track time in cgroup v2 freezer

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Message-ID: <aKiuHbu5NPSPcpYp@slm.duckdns.org>
Date: Fri, 22 Aug 2025 07:51:25 -1000
From: Tejun Heo <tj@...nel.org>
To: Tiffany Yang <ynaffit@...gle.com>
Cc: 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>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Koutný <mkoutny@...e.com>,
	"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>, Shuah Khan <shuah@...nel.org>,
	cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v4 0/2] cgroup: Track time in cgroup v2 freezer

On Thu, Aug 21, 2025 at 06:37:51PM -0700, Tiffany Yang wrote:
> Hello,
> 
> The cgroup v2 freezer controller is useful for freezing background
> applications so they don't contend with foreground tasks. However, this
> may disrupt any internal monitoring that the application is performing,
> as it may not be aware that it was frozen.
> 
> To illustrate, an application might implement a watchdog thread to
> monitor a high-priority task by periodically checking its state to
> ensure progress. The challenge is that the task only advances when the
> application is running, but watchdog timers are set relative to system
> time, not app time. If the app is frozen and misses the expected
> deadline, the watchdog, unaware of this pause, may kill a healthy
> process.
> 
> This series tracks the time that each cgroup spends "freezing" and
> exposes it via cgroup.stat.local. Include several basic selftests to
> demonstrate the expected behavior of this interface, including that:
>   1. Freeze time will increase while a cgroup is freezing, regardless of
>      whether it is frozen or not.
>   2. Each cgroup's freeze time is independent from the other cgroups in
>      its hierarchy.
> 
> Thanks,
> Tiffany
> 
> Signed-off-by: Tiffany Yang <ynaffit@...gle.com>

Applied to cgroup/for-6.18. Let's address further issues incrementally.

Thanks.

-- 
tejun