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

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Message-ID: <87a861a25y.fsf@concordia.ellerman.id.au>
Date:   Thu, 25 May 2017 16:19:53 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Michael Bringmann <mwb@...ux.vnet.ibm.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>
Cc:     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.ib>,
        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

Michael Bringmann <mwb@...ux.vnet.ibm.com> writes:

> On 05/24/2017 06:19 AM, Michael Ellerman wrote:
>> Michael Bringmann <mwb@...ux.vnet.ibm.com> writes:
>>>
>>> With or without 3af229f2071f, we would still need to add something, somewhere to add new
>>> bits to the 'node_possible_map'.  That is not being done.
>> 
>> You mustn't add bits to the possible map after boot.
>> 
>> That's its purpose, to tell you what nodes could ever *possibly* exist.
>
> The problem that I have been encountering is that the 'possible map' did *not*
> show all of the possible nodes.

OK so how did that happen?

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?

cheers