Don't warn about order-1 allocations with __GFP_NOFAIL

Traditionally, we never failed small orders (even regardless of any
__GFP_NOFAIL flags), and slab will allocate order-1 allocations even for
small allocations that could fit in a single page (in order to avoid
excessive fragmentation).

Maybe we should remove this warning entirely, but before making that
judgement, at least limit it to bigger allocations.

Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -1153,10 +1153,10 @@ again:
 			 * properly detect and handle allocation failures.
 			 *
 			 * We most definitely don't want callers attempting to
-			 * allocate greater than single-page units with
+			 * allocate greater than order-1 page units with
 			 * __GFP_NOFAIL.
 			 */
-			WARN_ON_ONCE(order > 0);
+			WARN_ON_ONCE(order > 1);
 		}
 		spin_lock_irqsave(&zone->lock, flags);
 		page = __rmqueue(zone, order, migratetype);