linux-kernel - Re: [PATCH RFC] cpuset: Make cpusets get restored on hotplug

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Date:   Thu, 26 Mar 2020 16:23:40 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Sonny Rao <sonnyrao@...gle.com>, Waiman Long <longman@...hat.com>,
        linux-kernel@...r.kernel.org, Dmitry Shmidt <dimitrysh@...gle.com>,
        Amit Pundir <amit.pundir@...aro.org>, kernel-team@...roid.com,
        Jesse Barnes <jsbarnes@...gle.com>, vpillai@...italocean.com,
        Peter Zijlstra <peterz@...radead.org>,
        Guenter Roeck <groeck@...omium.org>,
        Greg Kerr <kerrnel@...gle.com>, cgroups@...r.kernel.org,
        Johannes Weiner <hannes@...xchg.org>,
        Li Zefan <lizefan@...wei.com>
Subject: Re: [PATCH RFC] cpuset: Make cpusets get restored on hotplug

On Thu, Mar 26, 2020 at 04:18:59PM -0400, Tejun Heo wrote:
> On Thu, Mar 26, 2020 at 01:05:04PM -0700, Sonny Rao wrote:
> > I am surprised if anyone actually wants this behavior, we (Chrome OS)
> 
> The behavior is silly but consistent in that it doesn't allow empty active
> cpusets and it has been like that for many many years now.
> 
> > found out about it accidentally, and then found that Android had been
> > carrying a patch to fix it.  And if it were a desirable behavior then
> > why isn't it an option in v2?
> 
> Nobody is saying it's a good behavior (hence the change in cgroup2) and there
> are situations where changing things like this is justifiable, but, here:
> 
> * The proposed change makes the interface inconsistent and does so
>   unconditionally on what is now a mostly legacy interface.
> 
> * There already is a newer version of the interface which includes the
>   desired behavior.
> 
> * I forgot but as Waiman pointed out, you can even opt-in to the new
>   behavior, which is more comprehensive without the inconsitencies,
>   while staying on cgroup1.

Thank you Tejun, Waiman and Sonny. I confirmed the cgroup_v2_mode option
fixes cgroup v1's broken behavior.

We will use this mount option on our systems to fix it.

thanks,

 - Joel