mm/page_alloc: remove mistaken page == NULL check in rmqueue

If a page allocation fails, the ZONE_BOOSTER_WATERMARK should be tested,
cleared and kswapd woken whether the allocation attempt was via the PCP or
directly via the buddy list.

Remove the page == NULL so the ZONE_BOOSTED_WATERMARK bit is checked
unconditionally.  As it is unlikely that ZONE_BOOSTED_WATERMARK is set,
mark the branch accordingly.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Mel Gorman <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Tested-by: Yu Zhao <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: Marek Szyprowski <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Nicolas Saenz Julienne <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

mm/page_alloc.c

@@ -3781,12 +3781,10 @@ struct page *rmqueue(struct zone *preferred_zone,
 
 	page = rmqueue_buddy(preferred_zone, zone, order, alloc_flags,
 							migratetype);
-	if (unlikely(!page))
-		return NULL;
 
 out:
 	/* Separate test+clear to avoid unnecessary atomics */
-	if (test_bit(ZONE_BOOSTED_WATERMARK, &zone->flags)) {
+	if (unlikely(test_bit(ZONE_BOOSTED_WATERMARK, &zone->flags))) {
 		clear_bit(ZONE_BOOSTED_WATERMARK, &zone->flags);
 		wakeup_kswapd(zone, 0, 0, zone_idx(zone));
 	}