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

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Date:   Tue, 2 Feb 2021 14:56:49 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Yang Shi <shy828301@...il.com>, Oscar Salvador <osalvador@...e.de>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        David Rientjes <rientjes@...gle.com>,
        Huang Ying <ying.huang@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [RFC][PATCH 08/13] mm/migrate: demote pages during reclaim

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.