Currently the pseries machine code always attempts to set the size of the
guests's hash page table to 16MB.  However, because of the way the POWER
MMU works, a suitable hash page table size should really depend on memory
size.  16MB will be excessive for guests with <1GB and RAM, and may not be
enough for guests with >2GB of RAM (depending on guest page size and
other factors).

The usual given rule of thumb is that the hash table should be 1/64 of
the size of memory, but in fact the Linux guests we are aiming at don't
really need that much.  This patch, therefore, changes the hash table
allocation code to aim for 1/128 of the size of RAM (rounding up).  When
using KVM, this size may still be adjusted by the host kernel if it is
unable to allocate a suitable (contiguous) table.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>