linux-kernel - Re: [PATCH 0/2] cgroup-v2/freezer: small improvements

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Message-ID: <eamvrn5wbcdydffxfxitphfdfv3wec7wdsni3ykzvrammayndw@ecrksjfijhkh>
Date: Tue, 23 Dec 2025 18:29:23 +0100
From: Michal Koutný <mkoutny@...e.com>
To: Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
Cc: Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>, 
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] cgroup-v2/freezer: small improvements

On Tue, Dec 23, 2025 at 06:20:06PM +0800, Pavel Tikhomirov <ptikhomirov@...tuozzo.com> wrote:
> First allows freezing cgroups with kthreads inside, we still won't
> freeze kthreads, we still ignore them, but at the same time we allow
> cgroup to report frozen when all other non-kthread tasks are frozen.

kthreads in non-root cgroups are kind of an antipattern.
For which kthreads you would like this change? (See for instance the
commit d96c77bd4eeba ("KVM: x86: switch hugepage recovery thread to
vhost_task") as a possible refactoring of such threads.)

> Second patch adds information into dmesg to identify processes which
> prevent cgroup from being frozen or just don't allow it to freeze fast
> enough.

I can see how this can be useful for debugging, however, it resembles
the existing CONFIG_DETECT_HUNG_TASK and its
kernel.hung_task_timeout_secs. Could that be used instead?

Thanks,
Michal