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From: Michael Ellerman <mpe@ellerman.id.au>
To: Michael Bringmann <mwb@linux.vnet.ibm.com>,
        Reza Arbab <arbab@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, Paul Mackerras <paulus@samba.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Bharata B Rao <bharata@linux.vnet.ib>,
        Shailendra Singh <shailendras@nvidia.com>,
        Thomas Gleixner <tglx@linutronix.de>, linuxppc-dev@lists.ozlabs.org,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: Re: [Patch 2/2]: powerpc/hotplug/mm: Fix hot-add memory node assoc
In-Reply-To: <8e2417d8-d108-2949-40f2-997d53a3f367@linux.vnet.ibm.com>
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Date: Thu, 25 May 2017 16:19:53 +1000
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Michael Bringmann <mwb@linux.vnet.ibm.com> writes:

> On 05/24/2017 06:19 AM, Michael Ellerman wrote:
>> Michael Bringmann <mwb@linux.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