vmscan: do not evict inactive pages when skipping an active list scan

In AIM7 runs, recent kernels start swapping out anonymous pages well
before they should.  This is due to shrink_list falling through to
shrink_inactive_list if !inactive_anon_is_low(zone, sc), when all we
really wanted to do is pre-age some anonymous pages to give them extra
time to be referenced while on the inactive list.

The obvious fix is to make sure that shrink_list does not fall through to
scanning/reclaiming inactive pages when we called it to scan one of the
active lists.

This change should be safe because the loop in shrink_zone ensures that we
will still shrink the anon and file inactive lists whenever we should.

[kosaki.motohiro@jp.fujitsu.com: inactive_file_is_low() should be inactive_anon_is_low()]
Reported-by: Larry Woodman <lwoodman@redhat.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tomasz Chmielewski <mangoo@wpkg.org>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 6 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2ef59d5b16a6..04658189b9a5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1463,20 +1463,26 @@ static int inactive_file_is_low(struct zone *zone, struct scan_control *sc)
         return low;
 }
 
+static int inactive_list_is_low(struct zone *zone, struct scan_control *sc,
+                                int file)
+{
+        if (file)
+                return inactive_file_is_low(zone, sc);
+        else
+                return inactive_anon_is_low(zone, sc);
+}
+
 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
         struct zone *zone, struct scan_control *sc, int priority)
 {
         int file = is_file_lru(lru);
 
-        if (lru == LRU_ACTIVE_FILE && inactive_file_is_low(zone, sc)) {
-                shrink_active_list(nr_to_scan, zone, sc, priority, file);
+        if (is_active_lru(lru)) {
+                if (inactive_list_is_low(zone, sc, file))
+                    shrink_active_list(nr_to_scan, zone, sc, priority, file);
                 return 0;
         }
 
-        if (lru == LRU_ACTIVE_ANON && inactive_anon_is_low(zone, sc)) {
-                shrink_active_list(nr_to_scan, zone, sc, priority, file);
-                return 0;
-        }
         return shrink_inactive_list(nr_to_scan, zone, sc, priority, file);
 }