1 files changed, 33 insertions, 27 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index b0875871820d..2e8fbacd8744 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1718,26 +1718,6 @@ static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
 }
 
 /*
- * Smallish @nr_to_scan's are deposited in @nr_saved_scan,
- * until we collected @swap_cluster_max pages to scan.
- */
-static unsigned long nr_scan_try_batch(unsigned long nr_to_scan,
-				       unsigned long *nr_saved_scan)
-{
-	unsigned long nr;
-
-	*nr_saved_scan += nr_to_scan;
-	nr = *nr_saved_scan;
-
-	if (nr >= SWAP_CLUSTER_MAX)
-		*nr_saved_scan = 0;
-	else
-		nr = 0;
-
-	return nr;
-}
-
-/*
  * Determine how aggressively the anon and file LRU lists should be
  * scanned.  The relative value of each set of LRU lists is determined
  * by looking at the fraction of the pages scanned we did rotate back
@@ -1755,6 +1735,22 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc,
 	u64 fraction[2], denominator;
 	enum lru_list l;
 	int noswap = 0;
+	int force_scan = 0;
+
+
+	anon  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
+		zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
+	file  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
+		zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
+
+	if (((anon + file) >> priority) < SWAP_CLUSTER_MAX) {
+		/* kswapd does zone balancing and need to scan this zone */
+		if (scanning_global_lru(sc) && current_is_kswapd())
+			force_scan = 1;
+		/* memcg may have small limit and need to avoid priority drop */
+		if (!scanning_global_lru(sc))
+			force_scan = 1;
+	}
 
 	/* If we have no swap space, do not bother scanning anon pages. */
 	if (!sc->may_swap || (nr_swap_pages <= 0)) {
@@ -1765,11 +1761,6 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc,
 		goto out;
 	}
 
-	anon  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
-		zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
-	file  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
-		zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
-
 	if (scanning_global_lru(sc)) {
 		free  = zone_page_state(zone, NR_FREE_PAGES);
 		/* If we have very few page cache pages,
@@ -1836,8 +1827,23 @@ out:
 			scan >>= priority;
 			scan = div64_u64(scan * fraction[file], denominator);
 		}
-		nr[l] = nr_scan_try_batch(scan,
-					  &reclaim_stat->nr_saved_scan[l]);
+
+		/*
+		 * If zone is small or memcg is small, nr[l] can be 0.
+		 * This results no-scan on this priority and priority drop down.
+		 * For global direct reclaim, it can visit next zone and tend
+		 * not to have problems. For global kswapd, it's for zone
+		 * balancing and it need to scan a small amounts. When using
+		 * memcg, priority drop can cause big latency. So, it's better
+		 * to scan small amount. See may_noscan above.
+		 */
+		if (!scan && force_scan) {
+			if (file)
+				scan = SWAP_CLUSTER_MAX;
+			else if (!noswap)
+				scan = SWAP_CLUSTER_MAX;
+		}
+		nr[l] = scan;
 	}
 }