Re: [RFC][PATCH 08/13] mm/migrate: demote pages during reclaim

[Dave Hansen]

On 2/2/21 2:45 PM, Yang Shi wrote:
>> Should we keep it simple for now and only try to demote those pages that are
>> free of cpusets and memory policies?
>> Actually, demoting those pages to a CPU or a NUMA node that does not fall into
>> their set, would violate those constraints right?
> Yes, this has been discussed since the very beginning. There is not an
> easy way to figure out the memory placement policy (cpuset and
> mempolicy) from "page". I think this also prevents "demote those pages
> that are free of cpusets and memory policies".
> 
> The conclusion was the violation should be fine for now. And the
> demotion feature is opt'ed in by a new node reclaim mode.

This has come up a couple of times.

I'll add a bit of changelog material about it in the last patch since
that's where the opt-in is introduced.