linux-kernel - Re: [PATCH v5 3/3] mm/page_alloc: Keep memoryless cpuless node 0 offline

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Message-ID: <20200706160815.GH3448022@tassilo.jf.intel.com>
Date:   Mon, 6 Jul 2020 09:08:15 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Michal Suchánek <msuchanek@...e.de>,
        David Hildenbrand <david@...hat.com>,
        Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Satheesh Rajendran <sathnaga@...ux.vnet.ibm.com>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev@...ts.ozlabs.org, Christopher Lameter <cl@...ux.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v5 3/3] mm/page_alloc: Keep memoryless cpuless node 0
 offline

> > What's the point of this indirection other than another way of avoiding
> > empty node 0?
> 
> Honestly, I do not have any idea. I've traced it down to
> Author: Andi Kleen <ak@...e.de>
> Date:   Tue Jan 11 15:35:48 2005 -0800

I don't remember all the details, and I can't even find the commit
(is it in linux-historic?).

But AFAIK there's no guarantee PXMs are small and continuous, so it
seemed better to have a clean zero based space.

Back then we had a lot of problems with buggy SRAT tables in BIOS,
so we really tried to avoid trusting the BIOS as much as possible.

-Andi