This reverts commit e80ee884.

Pawel Sikora had a boot-time oops due to it - because the sign change
invalidates the following comparisons, since 'free_pages' can be
negative.

The micro-optimization just isn't worth it.
Bisected-by: NPawel Sikora <pluto@agmk.net>
Acked-by: NAndrew Morton <akpm@osdl.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>