linux-kernel - Re: [PATCH v3 1/2] cgroup: Show # of subsystem CSSes in cgroup.stat

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Message-ID: <c54651db-1a06-49f6-aea7-02768ad70756@redhat.com>
Date: Thu, 11 Jul 2024 15:13:12 -0400
From: Waiman Long <longman@...hat.com>
To: Tejun Heo <tj@...nel.org>
Cc: Johannes Weiner <hannes@...xchg.org>, Zefan Li <lizefan.x@...edance.com>,
 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 v3 1/2] cgroup: Show # of subsystem CSSes in cgroup.stat


On 7/11/24 14:59, Tejun Heo wrote:
> On Thu, Jul 11, 2024 at 02:51:38PM -0400, Waiman Long wrote:
>> On 7/11/24 14:44, Tejun Heo wrote:
>>> Hello,
>>>
>>> On Thu, Jul 11, 2024 at 01:39:38PM -0400, Waiman Long wrote:
>>>> On 7/11/24 13:18, Tejun Heo wrote:
>>> ...
>>>> Currently, I use the for_each_css() macro for iteration. If you mean
>>>> displaying all the possible cgroup subsystems even if they are not enabled
>>>> for the current cgroup, I will have to manually do the iteration.
>>> Just wrapping it with for_each_subsys() should do, no? for_each_css() won't
>>> iterate anything if css doesn't exist for the cgroup.
>> OK, I wasn't sure if you were asking to list all the possible cgroup v2
>> cgroup subsystems even if they weren't enabled in the current cgroup.
>> Apparently, that is the case. I prefer it that way too.
> Yeah, I think listing all is better. If the list corresponded directly to
> cgroup.controllers, it may make sense to only show enabled ones but we can
> have dying ones and implicitly enabled memory and so on, so I think it'd be
> cleaner to just list them all.

That will means cgroup subsystems that are seldomly used like rdma, misc 
or even hugetlb will always be shown in all the cgroup.stat output. I 
actually prefer just showing those that are enabled. As for dying memory 
cgroups, they will only be shown in its online ancestors. We currently 
don't know how many level down are each of the dying ones.

Cheers,
Longman