revert "memcg, vmscan: do not fall into reclaim-all pass too quickly"

Revert commit e975de9 ("memcg, vmscan: do not fall into reclaim-all
pass too quickly")

I merged this prematurely - Michal and Johannes still disagree about the
overall design direction and the future remains unclear.

Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -2176,11 +2176,10 @@ static inline bool should_continue_reclaim(struct zone *zone,
 	}
 }
 
-static int
+static void
 __shrink_zone(struct zone *zone, struct scan_control *sc, bool soft_reclaim)
 {
 	unsigned long nr_reclaimed, nr_scanned;
-	int groups_scanned = 0;
 
 	do {
 		struct mem_cgroup *root = sc->target_mem_cgroup;
@@ -2198,7 +2197,6 @@ __shrink_zone(struct zone *zone, struct scan_control *sc, bool soft_reclaim)
 		while ((memcg = mem_cgroup_iter_cond(root, memcg, &reclaim, filter))) {
 			struct lruvec *lruvec;
 
-			groups_scanned++;
 			lruvec = mem_cgroup_zone_lruvec(zone, memcg);
 
 			shrink_lruvec(lruvec, sc);
@@ -2226,28 +2224,15 @@ __shrink_zone(struct zone *zone, struct scan_control *sc, bool soft_reclaim)
 
 	} while (should_continue_reclaim(zone, sc->nr_reclaimed - nr_reclaimed,
 					 sc->nr_scanned - nr_scanned, sc));
-
-	return groups_scanned;
 }
 
 
 static void shrink_zone(struct zone *zone, struct scan_control *sc)
 {
 	bool do_soft_reclaim = mem_cgroup_should_soft_reclaim(sc);
 	unsigned long nr_scanned = sc->nr_scanned;
-	int scanned_groups;
 
-	scanned_groups = __shrink_zone(zone, sc, do_soft_reclaim);
-	/*
-	 * memcg iterator might race with other reclaimer or start from
-	 * a incomplete tree walk so the tree walk in __shrink_zone
-	 * might have missed groups that are above the soft limit. Try
-	 * another loop to catch up with others. Do it just once to
-	 * prevent from reclaim latencies when other reclaimers always
-	 * preempt this one.
-	 */
-	if (do_soft_reclaim && !scanned_groups)
-		__shrink_zone(zone, sc, do_soft_reclaim);
+	__shrink_zone(zone, sc, do_soft_reclaim);
 
 	/*
 	 * No group is over the soft limit or those that are do not have