mm/page_alloc: only search higher order when fallback

It seems unnecessary to search pages with order < alloc_order in
fallback allocation.

This can currently happen with ALLOC_NOFRAGMENT and alloc_order >
pageblock_order, so add a test to prevent it.

[vbabka@suse.cz: changelog addition]
Link: https://lkml.kernel.org/r/20220803025121.47018-1-wuyun.abel@bytedance.comSigned-off-by: Abel Wu <wuyun.abel@bytedance.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_alloc.c

@@ -3010,7 +3010,7 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype,
 	 * i.e. orders < pageblock_order. If there are no local zones free,
 	 * the zonelists will be reiterated without ALLOC_NOFRAGMENT.
 	 */
-	if (alloc_flags & ALLOC_NOFRAGMENT)
+	if (order < pageblock_order && alloc_flags & ALLOC_NOFRAGMENT)
 		min_order = pageblock_order;
 
 	/*