2 files changed, 34 insertions, 30 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2a00f17c3bf4..a4e1db3f1981 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4323,10 +4323,8 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
                 zone->zone_pgdat = pgdat;
 
                 zone_pcp_init(zone);
-                for_each_lru(l) {
+                for_each_lru(l)
                         INIT_LIST_HEAD(&zone->lru[l].list);
-                        zone->reclaim_stat.nr_saved_scan[l] = 0;
-                }
                 zone->reclaim_stat.recent_rotated[0] = 0;
                 zone->reclaim_stat.recent_rotated[1] = 0;
                 zone->reclaim_stat.recent_scanned[0] = 0;
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;
         }
 }