Re: [Qemu-devel] [RFC PATCH v2 2/2] spapr: Memory hot-unplug support

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

On Wed, Mar 16, 2016 at 12:36:05PM +1100, David Gibson wrote:
> On Tue, Mar 15, 2016 at 10:08:56AM +0530, Bharata B Rao wrote:
> > Add support to hot remove pc-dimm memory devices.
> > 
> > Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> 
> Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> 
> Looks correct, but again, needs to wait on the PAPR change.
> 
> Have you thought any further on the idea of sending an index message,
> then a count message as an interim approach to fixing this without
> requiring a PAPR change?

Removal by index and removal by count are valid messages by themselves
and drmgr would go ahead and start the removal in reponse to those
calls. IIUC, you are suggesting that lets remove one LMB by index in
response to 1st message and remove (count -1) LMBs from where the last
removal was done in the previous message.

Since the same code base of powerpc-utils works on PowerVM too, I am not
sure if such an approach would impact PowerVM in any undesirable manner.
May be Nathan can clarify ?

I see that this can be done, but the changes in drmgr code specially the
code related to LMB list handling/removal can be non-trivial. So not sure
if the temporary approach is all that worth here and hence I feel it is better
to wait and do it the count-indexed way.

While we are here, I would also like to get some opinion on the real
need for memory unplug. Is there anything that memory unplug gives us
which memory ballooning (shrinking mem via ballooning) can't give ?

Regards,
Bharata.