The likely() profiling tools show that __alloc_page() causes a lot of misses:

!       132    119193 __alloc_pages():mm/page_alloc.c@937

Because most __alloc_page() calls are not atomic.
Signed-off-by: NHua Zhong <hzhong@gmail.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>