This is the three-level page table support from the x86_64 patch.  It can
be enabled on x86, although it's not particularly needed at this point.
However, it can be used to implement very large physical memory (with
almost all of it in highmem) on UML.
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>