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

[David Gibson]

On Wed, Jun 01, 2016 at 12:18:22PM +0200, Thomas Huth wrote:
> 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 ?

I tend to agree.  I've held off on merging 2/2 pending outcome of this
discussion.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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