linux-kernel - Re: [Patch 2/2]: powerpc/hotplug/mm: Fix hot-add memory node assoc

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Message-Id: <20170525151011.m4ae4ipxbqsj3mn7@arbab-laptop.localdomain>
Date:   Thu, 25 May 2017 10:10:11 -0500
From:   Reza Arbab <arbab@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Balbir Singh <bsingharora@...il.com>
Cc:     Michael Bringmann <mwb@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Bharata B Rao <bharata@...ux.vnet.ibm.com>,
        Shailendra Singh <shailendras@...dia.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linuxppc-dev@...ts.ozlabs.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [Patch 2/2]: powerpc/hotplug/mm: Fix hot-add memory node assoc

On Thu, May 25, 2017 at 04:19:53PM +1000, Michael Ellerman wrote:
>The commit message for 3af229f2071f says:
>
>    In practice, we never see a system with 256 NUMA nodes, and in fact, we
>    do not support node hotplug on power in the first place, so the nodes
>    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>    that are online when we come up are the nodes that will be present for
>    the lifetime of this kernel.
>
>Is that no longer true?

I don't know what the reasoning behind that statement was at the time, 
but as far as I can tell, the only thing missing for node hotplug now is 
Balbir's patchset [1]. He fixes the resource issue which motivated 
3af229f2071f and reverts it.

With that set, I can instantiate a new numa node just by doing 
add_memory(nid, ...) where nid doesn't currently exist.

[1] https://lkml.kernel.org/r/1479253501-26261-1-git-send-email-bsingharora@gmail.com

-- 
Reza Arbab