Re: [LSF/MM/BPF TOPIC] [RFC PATCH 0/4] mm/mempolicy: introduce socket-aware weighted interleave

[Rakie Kim]

On Mon, 16 Mar 2026 15:45:24 -0400 Gregory Price <gourry@xxxxxxxxxx> wrote:
> On Mon, Mar 16, 2026 at 08:19:32AM -0700, Joshua Hahn wrote:
> > 
> > In that sense I thought the word "prefer" was a bit confusing, since I
> > thought it would mean that it would try to fulfill the alloactions
> > from within a packet first, then fall back to remote packets if that
> > failed. (Or maybe I am just misunderstanding your explanation. Please
> > do let me know if that is the case : -) )
> > 
> > If what I understand is the case , I think this is the same thing as
> > just restricting allocations to be socket-local. I also wonder if
> > this idea applies to other mempolicies as well (i.e. unweighted interleave)
> > 
> 
> I was thinking about this as well, and in my head i think you have to
> consider a 2x2 situation
> 
> cpuset             |   multi-socket-cpu      single-socket-cpu
> ==================================================================
> single-socket-mem  |     mem-package            mem-package
> ------------------------------------------------------------------
> multi-socket-mem   |       global                 global
> ------------------------------------------------------------------
> 
> But I think this reduces to cpuset nodes dictates the weights used -
> which should already be the case with the existing code.

Hello Gregory,

Thanks for your additional feedback.

I agree with your analysis. The final behavior should follow the nodes
dictated by the cpuset or mempolicy configurations.

> 
> I think you are right that we need to be very explicit about the
> fallback semantics here - but that may just be a matter of dictating
> whether the allocation falls back or prefers direct reclaim to push
> pages out of their requested nodes.
> 
> ~Gregory

As you and Joshua pointed out, making the fallback semantics explicit
is the most critical issue for this patch series. We need a clear policy
to decide whether the allocation should fall back to a remote node or
force direct reclaim to keep the allocation local.

I will explicitly define these fallback semantics and address this
trade-off in the design for the next version.

Thanks again for your time and review.

Rakie Kim