linux-kernel - Re: [PATCH 1/2] cgroup: Fix /proc/cgroups count for v2

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Date: Tue, 28 May 2024 23:42:13 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Tejun Heo <tj@...nel.org>
Cc: "T.J. Mercier" <tjmercier@...gle.com>, 
	Zefan Li <lizefan.x@...edance.com>, Johannes Weiner <hannes@...xchg.org>, shakeel.butt@...ux.dev, 
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] cgroup: Fix /proc/cgroups count for v2

On Tue, May 28, 2024 at 09:43:08AM GMT, Tejun Heo <tj@...nel.org> wrote:
> I agree that this can be a useful metric but am not sure /proc/cgroups is
> the right place to put it. Its use of v1 controller names, listing of
> controllers that don't exist in v2 and the unnecessary column are rather
> ugly and unnecessary.

At the same time, the info provided currently is incorrect or at least
misleading (when only v2 hierarchy is mounted, it mixes the counts) --
that's what T.J.'s patch attempts to rectify in my understanding.

> In v2, cgroup.controllers and cgroup.subtree_control govern which
> controllers are available and enabled in the subtree.

Yes, users could sum up cgroup.controllers contents for true v2
fingerprint.

> I think it would make sense to introduce something in a similar
> fashion. Can't think of a good name off the top of my head but add a
> cgroup. file which lists the controllers in the subtree along with the
> number of css's.

BTW, there is the 'debug' subsys that has (almost) exactly that:
'debug.csses' -- it's in v1 fashion though so it won't show hierarchical
sums.

Michal