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

[Waiman Long]

On 3/26/20 4:23 PM, Joel Fernandes wrote:
> 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already is a newer version of the interface which includes 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.
I am glad that it works for you.

I think the problem is that the v2_mode mount option is not that well
documented. Maybe I should send a patch to add some some description
about it in cgroup-v2.rst or cgroup-v1/cpusets.rst.

Cheers,
Longman