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

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Message-Id: <26b88035-b377-a594-0b7b-cfcf25e43e57@linux.vnet.ibm.com>
Date:   Wed, 14 Jun 2017 08:41:03 -0500
From:   Michael Bringmann <mwb@...ux.vnet.ibm.com>
To:     Balbir Singh <bsingharora@...il.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        "linux-kernel@...r.kernel.org" <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>,
        "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" 
        <linuxppc-dev@...ts.ozlabs.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Michael Bringmann from Kernel Team <mbringm@...ibm.com>
Subject: Re: RESEND Re: [Patch 2/2]: powerpc/hotplug/mm: Fix hot-add memory
 node assoc

Hello:

On 06/14/2017 12:27 AM, Balbir Singh wrote:
> On Wed, Jun 14, 2017 at 3:25 PM, Balbir Singh <bsingharora@...il.com> wrote:
>>
>>
>> On Wed, Jun 14, 2017 at 8:21 AM, Michael Bringmann <mwb@...ux.vnet.ibm.com>
>> wrote:
>>>
>>> On a related note, we are discussing the addition of 2 new device-tree
>>> properties
>>> with Pete Heyrman and his fellows that should simplify the determination
>>> of the
>>> set of required nodes.
>>>
>>> * One property would provide the total/max number of nodes needed by the
>>> kernel
>>>   on the current hardware.
>>
>>
> 
> Yes, that would be nice to have
> 
>>
>>>
>>> * A second property would provide the total/max number of nodes that the
>>> kernel
>>>   could use on any system to which it could be migrated.
>>>
>>
> 
> Not sure about this one, are you suggesting more memory can be added
> depending on the migration target?

We would use only one of these numbers to allocate nodes.  I have only been
on the periphery of the discussions, so I can not communicate the full
reasoning as to why both measures would be needed.  We would like to have
the first number for node allocation/initialization, but if only the second
value were provided, we would likely need to use it.

>>
>>
>>>
>>> These properties aren't available, yet, and it takes time to define new
>>> properties
>>> in the PAPR and have them implemented in pHyp and the kernel.  As an
>>> intermediary
>>> step, the systems which are doing a lot of dynamic hot-add/hot-remove
>>> configuration
>>> could provide equivalent information to the PowerPC kernel with a command
>>> line
>>> parameter.  The 'numa.c' code would then read this value and fill in the
>>> necessary
>>> entries in the 'node_possible_map'.
>>>
>>> Would you foresee any problems with using such a feature?
>>
>>
> 
> Sorry my mailer goofed up, resending
> 
> Balbir Singh
> 

Thanks.


-- 
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