Re: [Qemu-devel] [PATCH 21/27] pc: add memory hotplug 440fx machine

[Igor Mammedov]

On Fri, 22 Nov 2013 15:23:56 +0100
Gerd Hoffmann <address@hidden> wrote:

> On Do, 2013-11-21 at 03:38 +0100, Igor Mammedov wrote:
> > Add DimmBus for memory hotplug below 4Gb or above 4Gb depending
> > on initial memory size and hotplug memory size.
> > 
> > * if ram_size is less than 32-bit PCI hole start, reserve
> >   hotplug memory region as [ram_size,32bit-PCIhole-start)
> >   if hotplug memory region fits there,
> >   otherwise reserve hotplug memory region after "0x100000000ULL
> >   + above_4g_mem_size"
> 
> Hmm, 32-bit pci hole start depends on ram size ...
> 
> Does it make sense to hotplug memory above 4g unconditionally to
> simplify things?
It does and it was so in v6 RFC,
But it would rule out hotplug for 32-bit guests that doesn't support
more then 4Gb.

As use case 32-bit guest could start whit small initial memory
and hotplug additional memory if needed up to point where 32-bit
PCI hole starts. That would allow guests to launch with small amount
but baloon up upto 2-3.5 Gb depending on machine type.
I could drop 32-bit guest support and do only high mem hotplug if
this case it not interesting to the comunity, any suggestions?

I'm now experimenting with removing pci-info and allowing BIOS to
do placement of 32-bit PCI bars akin it was done with 64-bit BARs,
(I'm looking to using E820 reservations for it but I'm not sure it
will work with every guest OS, so it needs more testing).

> cheers,
>   Gerd
> 
> 
>