mm: page_alloc: only check the alloc flags and gfp_mask for dirty once

Currently it's calculated once per zone in the zonelist.
Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Jan Kara <jack@suse.cz>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -1917,6 +1917,8 @@ get_page_from_freelist(gfp_t gfp_mask, nodemask_t *nodemask, unsigned int order,
 	nodemask_t *allowednodes = NULL;/* zonelist_cache approximation */
 	int zlc_active = 0;		/* set if using zonelist_cache */
 	int did_zlc_setup = 0;		/* just call zlc_setup() one time */
+	bool consider_zone_dirty = (alloc_flags & ALLOC_WMARK_LOW) &&
+				(gfp_mask & __GFP_WRITE);
 
 	classzone_idx = zone_idx(preferred_zone);
 zonelist_scan:
@@ -1976,8 +1978,7 @@ get_page_from_freelist(gfp_t gfp_mask, nodemask_t *nodemask, unsigned int order,
 		 * will require awareness of zones in the
 		 * dirty-throttling and the flusher threads.
 		 */
-		if ((alloc_flags & ALLOC_WMARK_LOW) &&
-		    (gfp_mask & __GFP_WRITE) && !zone_dirty_ok(zone))
+		if (consider_zone_dirty && !zone_dirty_ok(zone))
 			continue;
 
 		mark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];