linux-kernel - Re: [PATCH v4 07/13] mm/mempolicy: handle MPOL_PREFERRED

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Message-ID: <YHbnwyITOehcVn0S@dhcp22.suse.cz>
Date:   Wed, 14 Apr 2021 15:01:55 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Feng Tang <feng.tang@...el.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dave Hansen <dave.hansen@...el.com>,
        Ben Widawsky <ben.widawsky@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v4 07/13] mm/mempolicy: handle MPOL_PREFERRED_MANY like
 BIND

On Wed 17-03-21 11:40:04, Feng Tang wrote:
> From: Ben Widawsky <ben.widawsky@...el.com>
> 
> Begin the real plumbing for handling this new policy. Now that the
> internal representation for preferred nodes and bound nodes is the same,
> and we can envision what multiple preferred nodes will behave like,
> there are obvious places where we can simply reuse the bind behavior.
> 
> In v1 of this series, the moral equivalent was:
> "mm: Finish handling MPOL_PREFERRED_MANY". Like that, this attempts to
> implement the easiest spots for the new policy. Unlike that, this just
> reuses BIND.

No, this is a bug step back. I think we really want to treat this as
PREFERRED. It doesn't have much to do with the BIND semantic at all.
At this stage there should be 2 things remaining - syscalls plumbing and
2 pass allocation request (optimistic preferred nodes restricted and
fallback to all nodes).
-- 
Michal Hocko
SUSE Labs