linux-kernel - Re: [PATCH-cgroup 1/2] cgroup: Show # of subsystem CSSes in /proc/cgroups

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Message-ID: <8527c0db-b3c1-46ba-86b5-6b3a776585b1@redhat.com>
Date: Mon, 8 Jul 2024 15:18:06 -0400
From: Waiman Long <longman@...hat.com>
To: Tejun Heo <tj@...nel.org>
Cc: Zefan Li <lizefan.x@...edance.com>, Johannes Weiner <hannes@...xchg.org>,
 cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH-cgroup 1/2] cgroup: Show # of subsystem CSSes in
 /proc/cgroups


On 7/8/24 15:05, Tejun Heo wrote:
> Hello,
>
> On Mon, Jul 08, 2024 at 03:01:39PM -0400, Waiman Long wrote:
>> That information is certainly useful to display to cgroup.stat which
>> currently only shows nr_descendants and nr_dying_descendants. So does
>> "nr_<subsys_name> <cnt>" for each cgroup subsystems look good to you or do
>> you have other suggestion?
> Yeah, something like that. Johannes, what do you think?
OK, will work on that.
>
>> The reason for this patch is because I got a bug report about leaking blkio
>> cgroup due to the information shown in /proc/cgroups. I know you want do
>> deprecate it for cgroup v2. How about adding a iine like "# Deprecated for
>> cgroup v2, use cgroup.stats file for cgroup counts" at the top of
>> /proc/cgroups when cgroup v2 is active?
> I wonder whether that would break some parsers but we can try that and see
> what happens.

I suppose the parser should skip line that begin with #. When testing 
this patch, I realize that systemd does parse /proc/cgroups when in 
cgroup v1 mode and change to it may break the bootup process. This file 
doesn't seem to be parsed at all when in cgroup v2 mode.

Cheers,
Longman