Move the watermark checking code into a single function.  Extend it to
account for the order of the allocation and the number of free pages that
could satisfy such a request.

From: Marcelo Tosatti <marcelo.tosatti@cyclades.com>

Fix typo in Nick's kswapd-high-order awareness patch
Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>