Re: [PATCH v2] cgroup/cpuset: rebind mm mempolicy to effective_mems, not mems_allowed
From: Waiman Long
Date: Tue Jun 16 2026 - 11:38:58 EST
On 6/16/26 9:44 AM, Gregory Price wrote:
On Tue, Jun 16, 2026 at 08:59:07AM +0200, David Hildenbrand (Arm) wrote:
On 6/16/26 05:43, Waiman Long wrote:I'm not grok'ing what is user-visible here.
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.
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?
The effective_mems and guarantee_online_mems() should be more or less equivalent for v2, but not for v1. In my response to David, I gave an example of how the behavior will differ.
Cheers,
Longman