mm: vmscan: fix force-scanning small targets without swap

commit a4d3e9e76337059406fcf3ead288c0df22a790e9 upstream.

Stable note: Not tracked in Bugzilla. This patch augments an earlier commit
        that avoids scanning priority being artificially raised. The older
	fix was particularly important for small memcgs to avoid calling
	wait_iff_congested() unnecessarily.

Without swap, anonymous pages are not scanned.  As such, they should not
count when considering force-scanning a small target if there is no swap.

Otherwise, targets are not force-scanned even when their effective scan
number is zero and the other conditions--kswapd/memcg--apply.

This fixes 246e87a93934 ("memcg: fix get_scan_count() for small
targets").

[akpm@linux-foundation.org: fix comment]
Signed-off-by: Johannes Weiner <jweiner@redhat.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Ying Han <yinghan@google.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 12 insertions, 15 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 130fa32441c..347bb4478f3 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1747,23 +1747,15 @@ 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;
+        bool force_scan = false;
         unsigned long nr_force_scan[2];
 
-
-        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;
-        }
+        /* kswapd does zone balancing and needs to scan this zone */
+        if (scanning_global_lru(sc) && current_is_kswapd())
+                force_scan = true;
+        /* memcg may have small limit and need to avoid priority drop */
+        if (!scanning_global_lru(sc))
+                force_scan = true;
 
         /* If we have no swap space, do not bother scanning anon pages. */
         if (!sc->may_swap || (nr_swap_pages <= 0)) {
@@ -1776,6 +1768,11 @@ 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,