Re: [Qemu-ppc] [RFC PATCH v0 0/2] Increase max memslots to 512 for PowerPC

[Thomas Huth]

On 01.06.2016 11:51, Bharata B Rao wrote:
> Recently the number of memory slots supported by KVM for PowerPC was changed
> from 32 to 512. QEMU was restricting the user specifiable hot-pluggable memory
> slots to 32. This patchset changes that to 512.
> 
> This allows more number of slots to be available for memory hotplugging.

It's certainly a good idea to increase the number of slots for
hot-pluggable memory. But should we really increase it to the full
maximum of 512 slots? The in-kernel slots are shared with other memory
regions, too, e.g. the memory slots for PCI cards. So if you allow the
users to plug all slots with DIMMs, they certainly will run into
problems there again later.

I think x86 is also using 256 DIMM slots only on purpose (see
https://lkml.org/lkml/2014/11/14/328 for example), so we should maybe
also limit the max. number of DIMM slots on spapr to
kvm_get_max_memslots() divided by two ?

 Thomas