thp: don't alloc harder for gfp nomemalloc even if nowait

Not worth throwing away the precious reserved free memory pool for
allocations that can fail gracefully (either through mempool or because
they're transhuge allocations later falling back to 4k allocations).

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -1971,7 +1971,12 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
 	alloc_flags |= (__force int) (gfp_mask & __GFP_HIGH);
 
 	if (!wait) {
-		alloc_flags |= ALLOC_HARDER;
+		/*
+		 * Not worth trying to allocate harder for
+		 * __GFP_NOMEMALLOC even if it can't schedule.
+		 */
+		if  (!(gfp_mask & __GFP_NOMEMALLOC))
+			alloc_flags |= ALLOC_HARDER;
 		/*
 		 * Ignore cpuset if GFP_ATOMIC (!wait) rather than fail alloc.
 		 * See also cpuset_zone_allowed() comment in kernel/cpuset.c.