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

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Message-ID: <alpine.DEB.2.22.394.2006291456550.27163@www.lameter.com>
Date:   Mon, 29 Jun 2020 14:58:40 +0000 (UTC)
From:   Christopher Lameter <cl@...ux.com>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.com>,
        Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Michael Ellerman <mpe@...erman.id.au>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Satheesh Rajendran <sathnaga@...ux.vnet.ibm.com>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH v5 3/3] mm/page_alloc: Keep memoryless cpuless node 0
 offline

On Wed, 24 Jun 2020, Srikar Dronamraju wrote:

> Currently Linux kernel with CONFIG_NUMA on a system with multiple
> possible nodes, marks node 0 as online at boot.  However in practice,
> there are systems which have node 0 as memoryless and cpuless.

Maybe add something to explain why you are not simply mapping the
existing memory to NUMA node 0 which is after all just a numbering scheme
used by the kernel and can be used arbitrarily?

This could be seen more as a bug in the arch code during the setup of NUMA
nodes. The two nodes are created by the firmwware / bootstrap code after
all. Just do not do it?