Re: [Qemu-devel] [PATCH 1/1] pc & q35: fix handling of lowmem

[Gerd Hoffmann]

On Do, 2014-02-27 at 15:01 -0500, Don Slutz wrote:
> Without this, asking for 3.25G on memory for pc-i440fx-2.0 does not
> adjust the pci hole to start at 3G.  Asking for 3.75G does do this
> adjustment.

This is intentional.

If we can fit all ram into low memory, because it is less than 3.5G,
we'll do that (pc machine type, q35 numbers are different but logic is
the same).  This way 32bit (+non-PAE) guests can continue to have up to
3.5G memory.

If we can't fit all ram into low memory (thus the guest should be able
to access ram above 4G anyway), then we'll cut off at a gigabyte
boundary (3G for pc machine type).  This way our ram is nicely
gigabyte-aligned and we can get best performance benefits from huge
pages.

The size of the pci hole changing in the second case is only a side
effect, it's not the main reason for the change.

cheers,
  Gerd