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 01:26:17PM +0200, David Hildenbrand (Arm) wrote:
> > 
> > Initial placement is only a starting point.  Pages initially allocated on
> > fast memory are not necessarily the long-term hot pages, and pages
> > initially allocated on slower memory may become hot as the workload's hot
> > set changes.  The policy therefore needs to be able to combine weighted
> > initial placement with memory tiering's NUMA fault based hot-page
> > promotion.
> 
> Ok, so memory allocation will respect the weights but balancing will ignore
> them? That really sounds rather odd to me.
> 
> And I assume that was the reason why we might have disallowed the combination:
> it turns a weighted mechanism into an unweighted mechanism.
> 
> So are we really sure these semantics that you would essentially set in stone
> here are the semantics we want? (ignoring weights)
>

Right, but you're requesting this configuration.  If you didn't set
F_NUMA_BALANCING then you get the existing semantics.

In the existing semantics, if we're INTERLEAVE and WEIGHTED_INTERLEAVE
we just always say "no tiering for you".

But as an opt-in option?  I don't quite see the argument for saying
interleaved regions (or tasks) to be opted-out if the user asks for it -
that just seems like an arbitrary limitation.

~Gregory