Re: [Qemu-devel] [PATCH v2] pc: allow raising low memory via max-ram-below-4g option

[Gerd Hoffmann]

  Hi,

> > +     *    qemu -M pc,max-ram-below-4g=2G -m 4G     -> 2048M low, 2048M high

> I assume max-ram-below-4g > 3.5G was unsupported before, and we
> are breaking compatibility intentionally.

max-ram-below-4g did only reduce memory, so max-ram-below-4g > 3.5G (or
max-ram-below-4g > 3G with gigabyte align) had no effect and therefore
is something pretty pointless.

I'd expect the one case quoted above to be the only case relevant in
practice (i.e. move split from 3G to 2G for more PCI I/O space),
especially given that the option was added after gigabyte alignment
support.

> Because this patch also
> changes the resulting memory layout when
>   3G < max_ram_below_4g < ram_size < 3.5G
> e.g.:
>   qemu -M pc,max-ram-below-4g=3200M -m 3328M

Ah, I see.  With the patch applied the gigabyte align option is weighed
higher, so qemu wouldn't give you 3200M lowmem.  I would be highly
surprised to see such a configuration in the wild ...

cheers,
  Gerd