[PATCH v4 1/8] mm: vmscan: add a map_nr_max field to shrinker_info

[Qi Zheng]

To prepare for the subsequent lockless memcg slab shrink,
add a map_nr_max field to struct shrinker_info to records
its own real shrinker_nr_max.

Suggested-by: Kirill Tkhai <tkhai@xxxxx>
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
 include/linux/memcontrol.h |  1 +
 mm/vmscan.c                | 41 ++++++++++++++++++++++----------------
 2 files changed, 25 insertions(+), 17 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index b6eda2ab205d..aa69ea98e2d8 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -97,6 +97,7 @@ struct shrinker_info {
 	struct rcu_head rcu;
 	atomic_long_t *nr_deferred;
 	unsigned long *map;
+	int map_nr_max;
 };
 
 struct lruvec_stats_percpu {
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 9414226218f0..2dcc01682026 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -224,9 +224,16 @@ static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
 					 lockdep_is_held(&shrinker_rwsem));
 }
 
+static inline bool need_expand(int new_nr_max, int old_nr_max)
+{
+	return round_up(new_nr_max, BITS_PER_LONG) >
+	       round_up(old_nr_max, BITS_PER_LONG);
+}
+
 static int expand_one_shrinker_info(struct mem_cgroup *memcg,
 				    int map_size, int defer_size,
-				    int old_map_size, int old_defer_size)
+				    int old_map_size, int old_defer_size,
+				    int new_nr_max)
 {
 	struct shrinker_info *new, *old;
 	struct mem_cgroup_per_node *pn;
@@ -240,12 +247,17 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
 		if (!old)
 			return 0;
 
+		/* Already expanded this shrinker_info */
+		if (!need_expand(new_nr_max, old->map_nr_max))
+			continue;
+
 		new = kvmalloc_node(sizeof(*new) + size, GFP_KERNEL, nid);
 		if (!new)
 			return -ENOMEM;
 
 		new->nr_deferred = (atomic_long_t *)(new + 1);
 		new->map = (void *)new->nr_deferred + defer_size;
+		new->map_nr_max = new_nr_max;
 
 		/* map: set all old bits, clear all new bits */
 		memset(new->map, (int)0xff, old_map_size);
@@ -295,6 +307,7 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
 		}
 		info->nr_deferred = (atomic_long_t *)(info + 1);
 		info->map = (void *)info->nr_deferred + defer_size;
+		info->map_nr_max = shrinker_nr_max;
 		rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
 	}
 	up_write(&shrinker_rwsem);
@@ -302,23 +315,14 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
 	return ret;
 }
 
-static inline bool need_expand(int nr_max)
-{
-	return round_up(nr_max, BITS_PER_LONG) >
-	       round_up(shrinker_nr_max, BITS_PER_LONG);
-}
-
 static int expand_shrinker_info(int new_id)
 {
 	int ret = 0;
-	int new_nr_max = new_id + 1;
+	int new_nr_max = round_up(new_id + 1, BITS_PER_LONG);
 	int map_size, defer_size = 0;
 	int old_map_size, old_defer_size = 0;
 	struct mem_cgroup *memcg;
 
-	if (!need_expand(new_nr_max))
-		goto out;
-
 	if (!root_mem_cgroup)
 		goto out;
 
@@ -332,7 +336,8 @@ static int expand_shrinker_info(int new_id)
 	memcg = mem_cgroup_iter(NULL, NULL, NULL);
 	do {
 		ret = expand_one_shrinker_info(memcg, map_size, defer_size,
-					       old_map_size, old_defer_size);
+					       old_map_size, old_defer_size,
+					       new_nr_max);
 		if (ret) {
 			mem_cgroup_iter_break(NULL, memcg);
 			goto out;
@@ -352,9 +357,11 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
 
 		rcu_read_lock();
 		info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
-		/* Pairs with smp mb in shrink_slab() */
-		smp_mb__before_atomic();
-		set_bit(shrinker_id, info->map);
+		if (!WARN_ON_ONCE(shrinker_id >= info->map_nr_max)) {
+			/* Pairs with smp mb in shrink_slab() */
+			smp_mb__before_atomic();
+			set_bit(shrinker_id, info->map);
+		}
 		rcu_read_unlock();
 	}
 }
@@ -432,7 +439,7 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg)
 	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++) {
+		for (i = 0; i < child_info->map_nr_max; i++) {
 			nr = atomic_long_read(&child_info->nr_deferred[i]);
 			atomic_long_add(nr, &parent_info->nr_deferred[i]);
 		}
@@ -899,7 +906,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 	if (unlikely(!info))
 		goto unlock;
 
-	for_each_set_bit(i, info->map, shrinker_nr_max) {
+	for_each_set_bit(i, info->map, info->map_nr_max) {
 		struct shrink_control sc = {
 			.gfp_mask = gfp_mask,
 			.nid = nid,
-- 
2.20.1