Re: [PATCH part5 0/7] Arrange hotpluggable memory as ZONE_MOVABLE.

[KOSAKI Motohiro <kosaki.motohiro@gmail.com>]

(8/12/13 1:23 PM), H. Peter Anvin wrote:
> On 08/12/2013 10:01 AM, Tang Chen wrote:
>>>
>>>> I'm just thinking of a more extreme case. For example, if a machine
>>>> has only one node hotpluggable, and the kernel resides in that node.
>>>> Then the system has no hotpluggable node.
>>>
>>> Yeah, sure, then there's no way that node can be hotpluggable and the
>>> right thing to do is booting up the machine and informing the userland
>>> that memory is not hotpluggable.
>>>
>>>> If we can prevent the kernel from using hotpluggable memory, in such
>>>> a machine, users can still do memory hotplug.
>>>>
>>>> I wanted to do it as generic as possible. But yes, finding out the
>>>> nodes the kernel resides in and make it unhotpluggable can work.
>>>
>>> Short of being able to remap memory under the kernel, I don't think
>>> this can be very generic and as a compromise trying to keep as many
>>> hotpluggable nodes as possible doesn't sound too bad.
>>
>> I think making one of the node hotpluggable is better. But OK, it is
>> no big deal. There won't be such machine in reality, I think. :)
>>
>
> The user may very well have configured a system with mirrored memory for
> the kernel node as that will be non-hotpluggable, but not for the
> others.  One can wonder how much that actually buys in real life, but
> still...

Note. Such system is much cheaper than full memory mirroring system. That's
one of reason why server vendors are interesting in hot plugging.