I find __free_pages_bulk very hard to understand ...  (I was trying to mod
it for the non MAX_ORDER aligned zones, and cleaned it up first).  This
should make it much more comprehensible to mortal man ...  I benchmarked
the changes on the big 16x and it's no slower (actually it's about 0.5%
faster, but that's within experimental error).

I moved the creation of mask into __free_pages_bulk from the caller - it
seems to really belong inside there.  Then instead of doing wierd limbo
dances with mask, I made it use order instead where it's more intuitive.
Personally I find this makes the whole thing a damned sight easier to
understand.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>