On 08/03/2012 11:22 AM, Michal Hocko wrote:

On Thu 02-08-12 14:24:18, Ying Han wrote:
[...]

quoted

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3e0d0cd..88487b3 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c

@@ -1866,7 +1866,22 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc)
  	do {
  		struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);

-		shrink_lruvec(lruvec, sc);
+		/*
+		 * Reclaim from mem_cgroup if any of these conditions are met:
+		 * - this is a targetted reclaim ( not global reclaim)
+		 * - reclaim priority is less than DEF_PRIORITY
+		 * - mem_cgroup or its ancestor ( not including root cgroup)
+		 * exceeds its soft limit
+		 *
+		 * Note: The priority check is a balance of how hard to
+		 * preserve the pages under softlimit. If the memcgs of the
+		 * zone having trouble to reclaim pages above their softlimit,
+		 * we have to reclaim under softlimit instead of burning more
+		 * cpu cycles.
+		 */
+		if (!global_reclaim(sc) || sc->priority<  DEF_PRIORITY ||
+				mem_cgroup_over_soft_limit(memcg))
+			shrink_lruvec(lruvec, sc);

  		/*
  		 * Limit reclaim has historically picked one memcg and

I am thinking that we could add a constant for the priority
limit. Something like
#define MEMCG_LOW_SOFTLIMIT_PRIORITY	DEF_PRIORITY

Although it doesn't seem necessary at the moment, because there is just
one location where it matters but it could help in the future.
What do you think?

I am working on changing the code to find the "highest priority"
LRU and reclaim from that list first.  That will obviate the need
for such a change. However, the other cleanups and simplifications
made by Ying's patch are good to have...

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