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

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Message-Id: <0def3557-7296-916a-f7d5-441cf5f1e00c@linux.vnet.ibm.com>
Date:   Fri, 26 May 2017 07:31:51 -0500
From:   Michael Bringmann <mwb@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Balbir Singh <bsingharora@...il.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.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

I am running into this problem on PowerPC systems where Balbir's patch set
was targeted.  So, yes, I do need to be able to add/enable a new numa node
during system execution in cases where more resources (memory, virtual
processors) are added to the system dynamically.

On 05/25/2017 10:46 PM, Michael Ellerman wrote:
> 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
> 
> 

-- 
Michael W. Bringmann
Linux Technology Center
IBM Corporation
Tie-Line  363-5196
External: (512) 286-5196
Cell:       (512) 466-0650
mwb@...ux.vnet.ibm.com