[PATCH] mmotm: memcg-mm-introduce-lowlimit-reclaim-fix.patch

[Michal Hocko]

mem_cgroup_reclaim_eligible -> mem_cgroup_within_guarantee as suggested
by Johannes.
---
 include/linux/memcontrol.h |  6 +++---
 mm/memcontrol.c            | 15 ++++++++-------
 mm/vmscan.c                | 25 ++++++++++++++++---------
 3 files changed, 27 insertions(+), 19 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 6c59056f4bc6..c00ccc5f70b9 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -92,7 +92,7 @@ bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
 bool task_in_mem_cgroup(struct task_struct *task,
 			const struct mem_cgroup *memcg);
 
-extern bool mem_cgroup_reclaim_eligible(struct mem_cgroup *memcg,
+extern bool mem_cgroup_within_guarantee(struct mem_cgroup *memcg,
 		struct mem_cgroup *root);
 
 extern struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page);
@@ -291,10 +291,10 @@ static inline struct lruvec *mem_cgroup_page_lruvec(struct page *page,
 	return &zone->lruvec;
 }
 
-static inline bool mem_cgroup_reclaim_eligible(struct mem_cgroup *memcg,
+static inline bool mem_cgroup_within_guarantee(struct mem_cgroup *memcg,
 		struct mem_cgroup *root)
 {
-	return true;
+	return false;
 }
 
 static inline struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7a276c0d141e..58982d18f6ea 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2810,26 +2810,27 @@ static struct mem_cgroup *mem_cgroup_lookup(unsigned short id)
 }
 
 /**
- * mem_cgroup_reclaim_eligible - checks whether given memcg is eligible for the
- * reclaim
+ * mem_cgroup_within_guarantee - checks whether given memcg is within its
+ * memory guarantee
  * @memcg: target memcg for the reclaim
  * @root: root of the reclaim hierarchy (null for the global reclaim)
  *
- * The given group is reclaimable if it is above its low limit and the same
- * applies for all parents up the hierarchy until root (including).
+ * The given group is within its reclaim gurantee if it is below its low limit
+ * or the same applies for any parent up the hierarchy until root (including).
+ * Such a group might be excluded from the reclaim.
  */
-bool mem_cgroup_reclaim_eligible(struct mem_cgroup *memcg,
+bool mem_cgroup_within_guarantee(struct mem_cgroup *memcg,
 		struct mem_cgroup *root)
 {
 	do {
 		if (!res_counter_low_limit_excess(&memcg->res))
-			return false;
+			return true;
 		if (memcg == root)
 			break;
 
 	} while ((memcg = parent_mem_cgroup(memcg)));
 
-	return true;
+	return false;
 }
 
 struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0f428158254e..20ca95fbaebb 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2215,8 +2215,18 @@ static inline bool should_continue_reclaim(struct zone *zone,
 	}
 }
 
+/**
+ * __shrink_zone - shrinks a given zone
+ *
+ * @zone: zone to shrink
+ * @sc: scan control with additional reclaim parameters
+ * @force_memcg_guarantee: do not reclaim memcgs which are within their memory
+ * guarantee
+ *
+ * Returns the number of reclaimed memcgs.
+ */
 static unsigned __shrink_zone(struct zone *zone, struct scan_control *sc,
-		bool follow_low_limit)
+		bool force_memcg_guarantee)
 {
 	unsigned long nr_reclaimed, nr_scanned;
 	unsigned nr_scanned_groups = 0;
@@ -2236,12 +2246,9 @@ static unsigned __shrink_zone(struct zone *zone, struct scan_control *sc,
 		do {
 			struct lruvec *lruvec;
 
-			/*
-			 * Memcg might be under its low limit so we have to
-			 * skip it during the first reclaim round
-			 */
-			if (follow_low_limit &&
-					!mem_cgroup_reclaim_eligible(memcg, root)) {
+			/* Memcg might be protected from the reclaim */
+			if (force_memcg_guarantee &&
+					mem_cgroup_within_guarantee(memcg, root)) {
 				/*
 				 * It would be more optimal to skip the memcg
 				 * subtree now but we do not have a memcg iter
@@ -2289,8 +2296,8 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc)
 	if (!__shrink_zone(zone, sc, true)) {
 		/*
 		 * First round of reclaim didn't find anything to reclaim
-		 * because of low limit protection so try again and ignore
-		 * the low limit this time.
+		 * because of the memory guantees for all memcgs in the
+		 * reclaim target so try again and ignore guarantees this time.
 		 */
 		__shrink_zone(zone, sc, false);
 	}
-- 
2.0.0.rc0

-- 
Michal Hocko
SUSE Labs
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