Revert "mm, memcg: decouple e{low,min} state mutations from protection checks"revert-1b40dd

This reverts commit 1b40dd68e341c56a85b09e4de40733da9154e3fe.

3 files changed, 45 insertions, 43 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index e0bcef180672..47c9d4e0a402 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -47,6 +47,12 @@ enum memcg_memory_event {
 	MEMCG_NR_MEMORY_EVENTS,
 };
 
+enum mem_cgroup_protection {
+	MEMCG_PROT_NONE,
+	MEMCG_PROT_LOW,
+	MEMCG_PROT_MIN,
+};
+
 struct mem_cgroup_reclaim_cookie {
 	pg_data_t *pgdat;
 	unsigned int generation;
@@ -385,26 +391,8 @@ static inline unsigned long mem_cgroup_protection(struct mem_cgroup *root,
 		   READ_ONCE(memcg->memory.elow));
 }
 
-void mem_cgroup_calculate_protection(struct mem_cgroup *root,
-				     struct mem_cgroup *memcg);
-
-static inline bool mem_cgroup_below_low(struct mem_cgroup *memcg)
-{
-	if (mem_cgroup_disabled())
-		return false;
-
-	return READ_ONCE(memcg->memory.elow) >=
-		page_counter_read(&memcg->memory);
-}
-
-static inline bool mem_cgroup_below_min(struct mem_cgroup *memcg)
-{
-	if (mem_cgroup_disabled())
-		return false;
-
-	return READ_ONCE(memcg->memory.emin) >=
-		page_counter_read(&memcg->memory);
-}
+enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root,
+						struct mem_cgroup *memcg);
 
 int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask);
 
@@ -883,19 +871,10 @@ static inline unsigned long mem_cgroup_protection(struct mem_cgroup *root,
 	return 0;
 }
 
-static inline void mem_cgroup_calculate_protection(struct mem_cgroup *root,
-						   struct mem_cgroup *memcg)
-{
-}
-
-static inline bool mem_cgroup_below_low(struct mem_cgroup *memcg)
+static inline enum mem_cgroup_protection mem_cgroup_protected(
+	struct mem_cgroup *root, struct mem_cgroup *memcg)
 {
-	return false;
-}
-
-static inline bool mem_cgroup_below_min(struct mem_cgroup *memcg)
-{
-	return false;
+	return MEMCG_PROT_NONE;
 }
 
 static inline int mem_cgroup_charge(struct page *page, struct mm_struct *mm,
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2df9510b7d64..b681feccce49 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6333,15 +6333,21 @@ static unsigned long effective_protection(unsigned long usage,
  *
  * WARNING: This function is not stateless! It can only be used as part
  *          of a top-down tree iteration, not for isolated queries.
+ *
+ * Returns one of the following:
+ *   MEMCG_PROT_NONE: cgroup memory is not protected
+ *   MEMCG_PROT_LOW: cgroup memory is protected as long there is
+ *     an unprotected supply of reclaimable memory from other cgroups.
+ *   MEMCG_PROT_MIN: cgroup memory is protected
  */
-void mem_cgroup_calculate_protection(struct mem_cgroup *root,
-				     struct mem_cgroup *memcg)
+enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root,
+						struct mem_cgroup *memcg)
 {
 	unsigned long usage, parent_usage;
 	struct mem_cgroup *parent;
 
 	if (mem_cgroup_disabled())
-		return;
+		return MEMCG_PROT_NONE;
 
 	if (!root)
 		root = root_mem_cgroup;
@@ -6354,21 +6360,21 @@ void mem_cgroup_calculate_protection(struct mem_cgroup *root,
 	 * that special casing.
 	 */
 	if (memcg == root)
-		return;
+		return MEMCG_PROT_NONE;
 
 	usage = page_counter_read(&memcg->memory);
 	if (!usage)
-		return;
+		return MEMCG_PROT_NONE;
 
 	parent = parent_mem_cgroup(memcg);
 	/* No parent means a non-hierarchical mode on v1 memcg */
 	if (!parent)
-		return;
+		return MEMCG_PROT_NONE;
 
 	if (parent == root) {
 		memcg->memory.emin = READ_ONCE(memcg->memory.min);
 		memcg->memory.elow = memcg->memory.low;
-		return;
+		goto out;
 	}
 
 	parent_usage = page_counter_read(&parent->memory);
@@ -6381,6 +6387,14 @@ void mem_cgroup_calculate_protection(struct mem_cgroup *root,
 	WRITE_ONCE(memcg->memory.elow, effective_protection(usage, parent_usage,
 			memcg->memory.low, READ_ONCE(parent->memory.elow),
 			atomic_long_read(&parent->memory.children_low_usage)));
+
+out:
+	if (usage <= memcg->memory.emin)
+		return MEMCG_PROT_MIN;
+	else if (usage <= memcg->memory.elow)
+		return MEMCG_PROT_LOW;
+	else
+		return MEMCG_PROT_NONE;
 }
 
 /**
diff --git a/mm/vmscan.c b/mm/vmscan.c
index d96e18726751..4dbfa8dcb8dc 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2645,15 +2645,14 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
 		unsigned long reclaimed;
 		unsigned long scanned;
 
-		mem_cgroup_calculate_protection(target_memcg, memcg);
-
-		if (mem_cgroup_below_min(memcg)) {
+		switch (mem_cgroup_protected(target_memcg, memcg)) {
+		case MEMCG_PROT_MIN:
 			/*
 			 * Hard protection.
 			 * If there is no reclaimable memory, OOM.
 			 */
 			continue;
-		} else if (mem_cgroup_below_low(memcg)) {
+		case MEMCG_PROT_LOW:
 			/*
 			 * Soft protection.
 			 * Respect the protection only as long as
@@ -2665,6 +2664,16 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
 				continue;
 			}
 			memcg_memory_event(memcg, MEMCG_LOW);
+			break;
+		case MEMCG_PROT_NONE:
+			/*
+			 * All protection thresholds breached. We may
+			 * still choose to vary the scan pressure
+			 * applied based on by how much the cgroup in
+			 * question has exceeded its protection
+			 * thresholds (see get_scan_count).
+			 */
+			break;
 		}
 
 		reclaimed = sc->nr_reclaimed;