[PATCH V7 6/9] Implement the select_victim_node within memcg.

[Ying Han <yinghan@xxxxxxxxxx>]

This add the mechanism for background reclaim which we remember the
last scanned node and always starting from the next one each time.
The simple round-robin fasion provide the fairness between nodes for
each memcg.

changelog v6..v5:
1. fix the correct comment style.

changelog v5..v4:
1. initialize the last_scanned_node to MAX_NUMNODES.

changelog v4..v3:
1. split off from the per-memcg background reclaim patch.

Signed-off-by: Ying Han <yinghan@xxxxxxxxxx>
---
 include/linux/memcontrol.h |    3 +++
 mm/memcontrol.c            |   36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 0 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 9157c4d..7444738 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -83,6 +83,9 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem);
 extern struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page);
 extern struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
 extern int mem_cgroup_watermark_ok(struct mem_cgroup *mem, int charge_flags);
+extern int mem_cgroup_last_scanned_node(struct mem_cgroup *mem);
+extern int mem_cgroup_select_victim_node(struct mem_cgroup *mem,
+					const nodemask_t *nodes);
 
 bool mem_cgroup_kswapd_can_sleep(void);
 struct mem_cgroup *mem_cgroup_get_shrink_target(void);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 527ad9a..4696fd8 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -288,6 +288,12 @@ struct mem_cgroup {
 	 */
 	u64 high_wmark_distance;
 	u64 low_wmark_distance;
+
+	/*
+	 * While doing per cgroup background reclaim, we cache the
+	 * last node we reclaimed from
+	 */
+	int last_scanned_node;
 };
 
 /* Stuffs for move charges at task migration. */
@@ -1544,6 +1550,27 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
 }
 
 /*
+ * Visit the first node after the last_scanned_node of @mem and use that to
+ * reclaim free pages from.
+ */
+int
+mem_cgroup_select_victim_node(struct mem_cgroup *mem, const nodemask_t *nodes)
+{
+	int next_nid;
+	int last_scanned;
+
+	last_scanned = mem->last_scanned_node;
+	next_nid = next_node(last_scanned, *nodes);
+
+	if (next_nid == MAX_NUMNODES)
+		next_nid = first_node(*nodes);
+
+	mem->last_scanned_node = next_nid;
+
+	return next_nid;
+}
+
+/*
  * Check OOM-Killer is already running under our hierarchy.
  * If someone is running, return false.
  */
@@ -4753,6 +4780,14 @@ int mem_cgroup_watermark_ok(struct mem_cgroup *mem,
 	return ret;
 }
 
+int mem_cgroup_last_scanned_node(struct mem_cgroup *mem)
+{
+	if (!mem)
+		return -1;
+
+	return mem->last_scanned_node;
+}
+
 static int mem_cgroup_soft_limit_tree_init(void)
 {
 	struct mem_cgroup_tree_per_node *rtpn;
@@ -4828,6 +4863,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
 		res_counter_init(&mem->memsw, NULL);
 	}
 	mem->last_scanned_child = 0;
+	mem->last_scanned_node = MAX_NUMNODES;
 	INIT_LIST_HEAD(&mem->oom_notify);
 
 	if (parent)
-- 
1.7.3.1

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