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

[Reza Arbab]

On Fri, May 26, 2017 at 01:46:58PM +1000, Michael Ellerman wrote:
> Reza Arbab <arbab@xxxxxxxxxxxxxxxxxx> 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?

I don't know if anything currently tries to do this. My interest in 
having this working is so that in the future, our coherent gpu memory 
could be added as a distinct node by the device driver.

--
Reza Arbab