linux-kernel - Re: [PATCH-cgroup v4] cgroup: Show # of subsystem CSSes in cgroup.stat

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Message-ID: <1a4963c0-9c90-4488-b13b-92019494741d@redhat.com>
Date: Fri, 26 Jul 2024 16:42:00 -0400
From: Waiman Long <longman@...hat.com>
To: Michal Koutný <mkoutny@...e.com>
Cc: Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
 Johannes Weiner <hannes@...xchg.org>, Jonathan Corbet <corbet@....net>,
 cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, Kamalesh Babulal
 <kamalesh.babulal@...cle.com>, Roman Gushchin <roman.gushchin@...ux.dev>
Subject: Re: [PATCH-cgroup v4] cgroup: Show # of subsystem CSSes in
 cgroup.stat

On 7/26/24 16:40, Waiman Long wrote:
>
>
> On 7/26/24 04:19, Michal Koutný wrote:
>>>>> +	for_each_css(css, ssid, cgroup) {
>>>>> +		if ((BIT(ssid) & cgrp_dfl_inhibit_ss_mask) ||
>>>>> +		    (cgroup_subsys[ssid]->root !=  &cgrp_dfl_root))
>>>>> +			continue;
>>>> Is this taken? (Given cgroup.stat is only on the default hierarchy.)
>>> I am not sure what you are asking here. Since cgroup.stat is a cgroup v2
>>> only control file, it won't show subsystems that are bound to cgroup v1.
>> So, is the if (...) ever true? (The file won't exist on v1.)
>
> A mixed cgroup v1/v2 environment is allowed, though not encouraged. We 
> can have some cgroup controllers bound to cgroup v2 and the rests to 
> cgroup v1. It is in this case that cgroup.stat will only show those 
> that are with cgroup v2.
>
> Regards,
> Longman
>