Received-SPF: pass (google.com: domain of linux-kernel+bounces-193129-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Date: Tue, 28 May 2024 23:42:13 +0200
From: Michal =?utf-8?Q?Koutn=C3=BD?= <mkoutny@suse.com>
To: Tejun Heo <tj@kernel.org>
Cc: "T.J. Mercier" <tjmercier@google.com>, 
	Zefan Li <lizefan.x@bytedance.com>, Johannes Weiner <hannes@cmpxchg.org>, shakeel.butt@linux.dev, 
	cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] cgroup: Fix /proc/cgroups count for v2
Message-ID: <zrvsmkowongdaqcy3yqb6abh76utimen5ejrnkczd4uq3etesl@jv3xb4uso4yk>
References: <20240528163713.2024887-1-tjmercier@google.com>
 <ZlYzzFYd0KgUnlso@slm.duckdns.org>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <ZlYzzFYd0KgUnlso@slm.duckdns.org>

On Tue, May 28, 2024 at 09:43:08AM GMT, Tejun Heo <tj@kernel.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