As threatened, here's a patch that unifies the ia64 memory init and memmap 
codepaths by unconditionalizing the CONFIG_VIRTUAL_MEM_MAP code and making 
CONFIG_DISCONTIGMEM required.  It also allows building with CONFIG_SMP=n 
and/or CONFIG_NUMA=n.  The end result should be easier to understand and hack 
on, and should make things like memory hotplug that much easier since people 
will only have to worry about one code path instead of every combination of 
the three options.

Boot tested on sn2 with:
CONFIG_IA64_SGI_SN=y
CONFIG_NUMA=y
CONFIG_SMP=y
CONFIG_PREEMPT=y
and
CONFIG_IA64_GENERIC=y
CONFIG_NUMA=n
CONFIG_SMP=n
CONFIG_PREEMPT=n

Anyone have a problem with this?  Is it a reasonable thing to do?  Assuming 
everyone is ok with it, there's a bit more I could do to make things easier 
to understand and hack on (and hopefully harder to break), like moving more 
stuff into numa.c and consolidating a header file or two.

 arch/ia64/mm/contig.c            |  300 ------------------------------------
 b/arch/ia64/Kconfig              |   24 ---
 b/arch/ia64/kernel/Makefile      |    1
 b/arch/ia64/kernel/acpi.c        |   24 ++-
 b/arch/ia64/kernel/ia64_ksyms.c  |    2
 b/arch/ia64/kernel/numa.c        |   57 +++++++
 b/arch/ia64/kernel/setup.c       |    2
 b/arch/ia64/kernel/smpboot.c     |   41 -----
 b/arch/ia64/mm/Makefile          |    3
 b/arch/ia64/mm/discontig.c       |   93 ++++++++----
 b/arch/ia64/mm/fault.c           |    5
 b/arch/ia64/mm/init.c            |    5
 b/arch/ia64/mm/numa.c            |    7
 b/arch/ia64/sn/kernel/setup.c    |    1
 b/drivers/acpi/Kconfig           |    1
 b/include/asm-ia64/acpi.h        |    1
 b/include/asm-ia64/meminit.h     |   18 --
 b/include/asm-ia64/mmzone.h      |    5
 b/include/asm-ia64/nodedata.h    |    4
 b/include/asm-ia64/numa.h        |    9 -
 b/include/asm-ia64/page.h        |   16 --
 b/include/asm-ia64/pgtable.h     |   18 --
 b/include/asm-ia64/processor.h   |    4
 b/include/asm-ia64/smp.h         |    1
 b/include/asm-ia64/sn/sn_cpuid.h |    4
 b/include/linux/acpi.h           |    4
 26 files changed, 165 insertions(+), 485 deletions(-)

Thanks,
Jesse