This is just for internal review right now. I plan to send this out
in a few days if this is thought to be beneficial.

The virtual memory map on SGI machines is current mapped using
a part of the VMALLOC address space. This means that we are forced
to use page sized maps and each of these pages will require a TLB
entry if a page struct is in use. This can become quite frequent
since with one 16k page one can only map 256 pages. 256 pages in
turn mean 4 Megabytes.

In a large system with lets say 4GB of RAM per node we may have
to use 1024 TLBs. If an application frequently accesses page meta
information (typical for file operations and memory allocation
operations!) then we may create a problem.

The following patchset makes it possible to use larger page
sizes for the virtual memory map. If one would use a 16MB page size
then we would be able to access all the metainformation about
the page states in a 4GB area with a single TLB entry.

This patch also introduces a facility to provide areas that can
map pages of varying sizes called the VKP (variable kernel pagesizes).
The obvious first user is the virtual memory map but it may also be
used to map other large scale memory structures with just a few
TLBs and a small page table.