[PATCH] mm/page_alloc: cache the result of node_dirty_ok()

[Wonhyuk Yang <vvghjk1234@gmail.com>]

To spread dirty page, nodes are checked whether
it reached the dirty limit using the expensive
node_dirty_ok(). To reduce the number of calling
node_dirty_ok(), last node that hit the dirty
limit is cached.

Instead of caching the node, caching both node
and it's result of node_dirty_ok() can reduce
the number of calling node_dirty_ok() more than
before.

Signed-off-by: Wonhyuk Yang <vvghjk1234@gmail.com>
---
 mm/page_alloc.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0e42038382c1..aba62cf31a0e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4068,7 +4068,8 @@ 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_limit = false;
 	bool no_fallback;
 
 retry:
@@ -4107,13 +4108,13 @@ 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_limit = node_dirty_ok(zone->zone_pgdat);
+			}
 
-			if (!node_dirty_ok(zone->zone_pgdat)) {
-				last_pgdat_dirty_limit = zone->zone_pgdat;
+			if (!last_pgdat_dirty_limit)
 				continue;
-			}
 		}
 
 		if (no_fallback && nr_online_nodes > 1 &&
-- 
2.30.2