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

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Message-ID: <aD9_V1rSqqESFekK@slm.duckdns.org>
Date: Tue, 3 Jun 2025 13:03:51 -1000
From: Tejun Heo <tj@...nel.org>
To: Tiffany Yang <ynaffit@...gle.com>
Cc: linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	kernel-team@...roid.com, 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>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>
Subject: Re: [RFC PATCH] cgroup: Track time in cgroup v2 freezer

On Tue, Jun 03, 2025 at 10:43:05PM +0000, Tiffany Yang wrote:
> The cgroup v2 freezer controller allows user processes to be dynamically
> added to and removed from an interruptible frozen state from
> userspace. This feature is helpful for application management, as it
> allows background tasks to be frozen to prevent them from being
> scheduled or otherwise contending with foreground tasks for resources.
> Still, applications are usually unaware of their having been placed in
> the freezer cgroup, so any watchdog timers they may have set will fire
> when they exit. To address this problem, I propose tracking the per-task
> frozen time and exposing it to userland via procfs.

Just on a glance, it feels rather odd to be tracking this per task given
that the state is per cgroup. Can you account this per cgroup?

Thanks.

-- 
tejun