I've had ia32-discontigmem under test for a month, uneventfully.  Possibly
because I don't have a machine to test it on....

A major part of this work is a general move to convert the low-level
memory management to consistently use pageframe numbers.  It's a bit
schizo at present..

This patch was written by Martin Bligh.  A version of this patch is in
the 2.4 aa tree.

It changes the unsigned longs node_start_paddr and zone_start_paddr to
page frame numbers.  This is necessary because a PAE address is 36 bits
and cannot be represented in an unsigned long.

 - The per-node physical memory start address node_start_paddr becomes
   a pfn, node_start_pfn.

 - The per-zone physical memory start address zone_start_paddr becomes
   a pfn, zone_start_pfn.

 - free_area_init_node() takes a pfn rather than a physical address.

Patricia has tested this patch on the following configurations: UP,
SMP, SMP PAE, multiquad, multiquad PAE, multiquad DISCONTIGMEM,
multiquad DISCONTIGMEM PAE.