vmscan: handle may_swap more strictly

Commit 2e2e425989080cc534fc0fca154cae515f971cf5 ("vmscan,memcg:
reintroduce sc->may_swap) add may_swap flag and handle it at
get_scan_ratio().

But the result of get_scan_ratio() is ignored when priority == 0, so anon
lru is scanned even if may_swap == 0 or nr_swap_pages == 0.  IMHO, this is
not an expected behavior.

As for memcg especially, because of this behavior many and many pages are
swapped-out just in vain when oom is invoked by mem+swap limit.

This patch is for handling may_swap flag more strictly.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index f3a55d1..057e44b 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1430,13 +1430,6 @@ static void get_scan_ratio(struct zone *zone, struct scan_control *sc,
        unsigned long ap, fp;
        struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
 
-       /* If we have no swap space, do not bother scanning anon pages. */
-       if (!sc->may_swap || (nr_swap_pages <= 0)) {
-               percent[0] = 0;
-               percent[1] = 100;
-               return;
-       }
-
        anon  = zone_nr_pages(zone, sc, LRU_ACTIVE_ANON) +
                zone_nr_pages(zone, sc, LRU_INACTIVE_ANON);
        file  = zone_nr_pages(zone, sc, LRU_ACTIVE_FILE) +
@@ -1534,15 +1527,22 @@ static void shrink_zone(int priority, struct zone *zone,
        enum lru_list l;
        unsigned long nr_reclaimed = sc->nr_reclaimed;
        unsigned long swap_cluster_max = sc->swap_cluster_max;
+       int noswap = 0;
 
-       get_scan_ratio(zone, sc, percent);
+       /* If we have no swap space, do not bother scanning anon pages. */
+       if (!sc->may_swap || (nr_swap_pages <= 0)) {
+               noswap = 1;
+               percent[0] = 0;
+               percent[1] = 100;
+       } else
+               get_scan_ratio(zone, sc, percent);
 
        for_each_evictable_lru(l) {
                int file = is_file_lru(l);
                unsigned long scan;
 
                scan = zone_nr_pages(zone, sc, l);
-               if (priority) {
+               if (priority || noswap) {
                        scan >>= priority;
                        scan = (scan * percent[file]) / 100;
                }