On 06/23/2015 11:01 PM, Bharata B Rao wrote:

So will it be correct to say that memory hotplug to memory-less node
isn't supported by PowerPC kernel ? Should I enforce the same in QEMU
for PowerKVM ?

I'm not sure if that is correct. It appears that we initialize all online
nodes, even those without spanned_pages, at boot time. This occurs
in setup_node_data() called from initmem_init().

Looking at this I would think that we could add memory to any online node
even if it does not have any spanned_pages. I think an interesting test
we be to check for the node being online instead of checking to see if
it has any memory.

-Nathan

On Mon, Jun 22, 2015 at 10:18 AM, Bharata B Rao [off-list ref] wrote:

quoted

Hi,

While developing memory hotplug support in QEMU for PoweKVM, I
realized that guest kernel has specific checks to prevent hot addition
of memory to a memory-less node.

I am referring to arch/powerpc/mm/numa.c:hot_add_scn_to_nid() which
has explicit checks to ensure that it returns a nid that has some some
memory (NODE_DATA(nid)->node_spanned_pages) even when user wants to
hotplug to a node that currently has zero memory.

Is this limitation by design ?

Regards,
Bharata.
--
http://raobharata.wordpress.com/