list_lru: get rid of ->active_nodes

The active_nodes mask allows us to skip empty nodes when walking over
list_lru items from all nodes in list_lru_count/walk. However, these
functions are never called from hot paths, so it doesn't seem we need
such kind of optimization there. OTOH, removing the mask will make it
easier to make list_lru per-memcg.

Signed-off-by: Vladimir Davydov <[e-mail]>
Cc: Dave Chinner <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Greg Thelen <[e-mail]>
Cc: Glauber Costa <[e-mail]>
Cc: Alexander Viro <[e-mail]>
Cc: Christoph Lameter <[e-mail]>
Cc: Pekka Enberg <[e-mail]>
Cc: David Rientjes <[e-mail]>
Cc: Joonsoo Kim <[e-mail]>
Cc: Tejun Heo <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/list_lru.h

···
 
 struct list_lru {
 	struct list_lru_node	*node;
-	nodemask_t		active_nodes;
 };
 
 void list_lru_destroy(struct list_lru *lru);
···
 	long count = 0;
 	int nid;
 
-	for_each_node_mask(nid, lru->active_nodes)
+	for_each_node_state(nid, N_NORMAL_MEMORY)
 		count += list_lru_count_node(lru, nid);
 
 	return count;
···
 	long isolated = 0;
 	int nid;
 
-	for_each_node_mask(nid, lru->active_nodes) {
+	for_each_node_state(nid, N_NORMAL_MEMORY) {
 		isolated += list_lru_walk_node(lru, nid, isolate,
 					       cb_arg, &nr_to_walk);
 		if (nr_to_walk <= 0)

mm/list_lru.c

···
 	WARN_ON_ONCE(nlru->nr_items < 0);
 	if (list_empty(item)) {
 		list_add_tail(item, &nlru->list);
-		if (nlru->nr_items++ == 0)
-			node_set(nid, lru->active_nodes);
+		nlru->nr_items++;
 		spin_unlock(&nlru->lock);
 		return true;
 	}
···
 	spin_lock(&nlru->lock);
 	if (!list_empty(item)) {
 		list_del_init(item);
-		if (--nlru->nr_items == 0)
-			node_clear(nid, lru->active_nodes);
+		nlru->nr_items--;
 		WARN_ON_ONCE(nlru->nr_items < 0);
 		spin_unlock(&nlru->lock);
 		return true;
···
 		case LRU_REMOVED_RETRY:
 			assert_spin_locked(&nlru->lock);
 		case LRU_REMOVED:
-			if (--nlru->nr_items == 0)
-				node_clear(nid, lru->active_nodes);
+			nlru->nr_items--;
 			WARN_ON_ONCE(nlru->nr_items < 0);
 			isolated++;
 			/*
···
 	if (!lru->node)
 		return -ENOMEM;
 
-	nodes_clear(lru->active_nodes);
 	for (i = 0; i < nr_node_ids; i++) {
 		spin_lock_init(&lru->node[i].lock);
 		if (key)