On Fri, May 26, 2017 at 01:46:58PM +1000, Michael Ellerman wrote:

Reza Arbab [off-list ref] writes:

quoted

On Thu, May 25, 2017 at 04:19:53PM +1000, Michael Ellerman wrote:

quoted

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