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

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Message-ID: <87zie08ekt.fsf@concordia.ellerman.id.au>
Date:   Fri, 26 May 2017 13:46:58 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Reza Arbab <arbab@...ux.vnet.ibm.com>,
        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

Reza Arbab <arbab@...ux.vnet.ibm.com> writes:

> 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.

But does that actually happen on any real system?

cheers