Re: [PATCH v2] cgroup/cpuset: rebind mm mempolicy to effective_mems, not mems_allowed

[Gregory Price]

On Tue, Jun 16, 2026 at 08:59:07AM +0200, David Hildenbrand (Arm) wrote:
> On 6/16/26 05:43, Waiman Long wrote:
> > On 6/15/26 10:26 PM, Waiman Long wrote:
> >>
> >>
> >> The reason why I am suggesting to use cs->effective_mems to keep the old
> >> cgroup v1 behavior. If the consensus is to use the output of
> >> guarantee_online_mems() for mpol_rebind_mm(), I will not be against that but
> >> it will be a slight change in user-visible behavior.

I'm not grok'ing what is user-visible here.

The two values should effectively be equivalent because we're
using this value to constrain mpol's during a hotplug event.

If the values differed, you would be saying there's a race condition
that could affect correctness of the rebind (which can't happen,
because this whole thing is done under the hotplug lock btw).

Can you help me understand?

~Gregory