[v4 PATCH 10/11] mm: memcontrol: reparent nr_deferred when memcg offline

[Yang Shi <shy828301@gmail.com>]

Now shrinker's nr_deferred is per memcg for memcg aware shrinkers, add to parent's
corresponding nr_deferred when memcg offline.

Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 include/linux/memcontrol.h |  1 +
 mm/memcontrol.c            |  1 +
 mm/vmscan.c                | 31 +++++++++++++++++++++++++++++++
 3 files changed, 33 insertions(+)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index e0384367e07d..fe1375f08881 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1586,6 +1586,7 @@ extern int alloc_shrinker_info(struct mem_cgroup *memcg);
 extern void free_shrinker_info(struct mem_cgroup *memcg);
 extern void set_shrinker_bit(struct mem_cgroup *memcg,
 			     int nid, int shrinker_id);
+extern void reparent_shrinker_deferred(struct mem_cgroup *memcg);
 #else
 #define mem_cgroup_sockets_enabled 0
 static inline void mem_cgroup_sk_alloc(struct sock *sk) { };
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 65d9eb0215b5..cccf2bacb147 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5284,6 +5284,7 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
 	page_counter_set_low(&memcg->memory, 0);
 
 	memcg_offline_kmem(memcg);
+	reparent_shrinker_deferred(memcg);
 	wb_memcg_offline(memcg);
 
 	drain_all_stock(memcg);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index ea1402e7b968..e73f200ffd2d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -383,6 +383,37 @@ static long set_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
 	return atomic_long_add_return(nr, &info->nr_deferred[shrinker->id]);
 }
 
+static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
+						     int nid)
+{
+	return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
+					 lockdep_is_held(&shrinker_rwsem));
+}
+
+void reparent_shrinker_deferred(struct mem_cgroup *memcg)
+{
+	int i, nid;
+	long nr;
+	struct mem_cgroup *parent;
+	struct shrinker_info *child_info, *parent_info;
+
+	parent = parent_mem_cgroup(memcg);
+	if (!parent)
+		parent = root_mem_cgroup;
+
+	/* Prevent from concurrent shrinker_info expand */
+	down_read(&shrinker_rwsem);
+	for_each_node(nid) {
+		child_info = shrinker_info_protected(memcg, nid);
+		parent_info = shrinker_info_protected(parent, nid);
+		for (i = 0; i < shrinker_nr_max; i++) {
+			nr = atomic_long_read(&child_info->nr_deferred[i]);
+			atomic_long_add(nr, &parent_info->nr_deferred[i]);
+		}
+	}
+	up_read(&shrinker_rwsem);
+}
+
 static bool cgroup_reclaim(struct scan_control *sc)
 {
 	return sc->target_mem_cgroup;
-- 
2.26.2