Re: [PATCH] mm/numa_balancing: allow migrate on protnone reference with MPOL_WEIGHTED_INTERLEAVE policy

[Gregory Price <gourry@gourry.net>]

On Wed, Sep 30, 2026 at 04:59:50PM +0800, Li Zhe wrote:
> On 9/30/26 4:43 PM, Gregory Price wrote:
> > On Wed, Sep 30, 2026 at 03:26:17PM +0800, Li Zhe wrote:
> >> Allow MPOL_F_NUMA_BALANCING for MPOL_WEIGHTED_INTERLEAVE.  As with
> >> MPOL_BIND and MPOL_PREFERRED_MANY, keep migration constrained by the
> >> policy nodemask: if the CPU's node is outside the nodemask, do not
> >> migrate the folio there.
> >>
> > Why for WEIGHTED_INTERLEAVE and not INTERLEAVE as well?
> 
> 
> Thanks for pointing this out.
> 
> I focused on MPOL_WEIGHTED_INTERLEAVE in v1 because the motivating use
> case is to seed memory across tiers with a configurable ratio at
> allocation time, and then let NUMA balancing/memory tiering adjust the
> placement based on access patterns. With equal weights,
> MPOL_WEIGHTED_INTERLEAVE can also cover the regular interleave
> allocation pattern.
> 
> That said, I agree that MPOL_INTERLEAVE can be handled consistently as
> well. Since this is still an explicit opt-in via MPOL_F_NUMA_BALANCING,
> unless others see a reason to keep MPOL_INTERLEAVE out, I will extend
> this in v2 to cover both MPOL_INTERLEAVE and MPOL_WEIGHTED_INTERLEAVE
> with the same nodemask constraint.
> 

Looking at it, is there an actual reason to limit F_MORON at all? Or
should we just lift

                if (pol->flags & MPOL_F_MORON) {
                        /*
                         * Optimize placement among multiple nodes
                         * via NUMA balancing
                         */
                        if (node_isset(thisnid, pol->nodes))
                                break;
                        goto out;
                }

Out ahead of everything?

~Gregory