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

[Joel Fernandes <joel-QYYGw3jwrUn5owFQY34kdNi2O/JbrIOy@public.gmane.org>]

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 * There already is a newer version of the interface which includes the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