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

[Rik van Riel <riel@redhat.com>]

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.


Reported-by: Larry Woodman <lwoodman@redhat.com>
Signed-off-by: Rik van Riel <riel@redhat.com>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 777af57..ec4dfda 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1469,13 +1469,15 @@ static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
 {
 	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 (lru == LRU_ACTIVE_FILE) {
+		if (inactive_file_is_low(zone, sc))
+		      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);
+	if (lru == LRU_ACTIVE_ANON) {
+		if (inactive_file_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);

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