mm/page_alloc: cache the result of node_dirty_ok()

To spread dirty pages, nodes are checked whether they have reached the
dirty limit using the expensive node_dirty_ok().  To reduce the frequency
of calling node_dirty_ok(), the last node that hit the dirty limit can be
cached.

Instead of caching the node, caching both the node and its node_dirty_ok()
status can reduce the number of calle to node_dirty_ok().

[akpm@linux-foundation.org: rename last_pgdat_dirty_limit to last_pgdat_dirty_ok]
Link: https://lkml.kernel.org/r/20220430011032.64071-1-vvghjk1234@gmail.comSigned-off-by: Wonhyuk Yang <vvghjk1234@gmail.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Donghyeok Kim <dthex5d@gmail.com>
Cc: JaeSang Yoo <jsyoo5b@gmail.com>
Cc: Jiyoup Kim <lakroforce@gmail.com>
Cc: Ohhoon Kwon <ohkwon1043@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_alloc.c

@@ -4021,7 +4021,8 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
 {
 	struct zoneref *z;
 	struct zone *zone;
-	struct pglist_data *last_pgdat_dirty_limit = NULL;
+	struct pglist_data *last_pgdat = NULL;
+	bool last_pgdat_dirty_ok = false;
 	bool no_fallback;
 
 retry:
@@ -4060,13 +4061,13 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
 		 * dirty-throttling and the flusher threads.
 		 */
 		if (ac->spread_dirty_pages) {
-			if (last_pgdat_dirty_limit == zone->zone_pgdat)
-				continue;
+			if (last_pgdat != zone->zone_pgdat) {
+				last_pgdat = zone->zone_pgdat;
+				last_pgdat_dirty_ok = node_dirty_ok(zone->zone_pgdat);
+			}
 
-			if (!node_dirty_ok(zone->zone_pgdat)) {
-				last_pgdat_dirty_limit = zone->zone_pgdat;
+			if (!last_pgdat_dirty_ok)
 				continue;
-			}
 		}
 
 		if (no_fallback && nr_online_nodes > 1 &&