mm/list_lru: don't pass unnecessary key parameters

Patch series "mm/list_lru: Split list_lru lock into per-cgroup scope".

When LOCKDEP is not enabled, lock_class_key is an empty struct that is
never used.  But the list_lru initialization function still takes a
placeholder pointer as parameter, and the compiler cannot optimize it
because the function is not static and exported.

Remove this parameter and move it inside the list_lru struct.  Only use it
when LOCKDEP is enabled.  Kernel builds with LOCKDEP will be slightly
larger, while !LOCKDEP builds without it will be slightly smaller (the
common case).

Link: https://lkml.kernel.org/r/20241104175257.60853-1-ryncsn@gmail.com
Link: https://lkml.kernel.org/r/20241104175257.60853-2-ryncsn@gmail.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Chengming Zhou <zhouchengming@bytedance.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Waiman Long <longman@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: ryncsn

include/linux/list_lru.h

@@ -56,16 +56,28 @@ struct list_lru {
 	bool			memcg_aware;
 	struct xarray		xa;
 #endif
+#ifdef CONFIG_LOCKDEP
+	struct lock_class_key	*key;
+#endif
 };
 
 void list_lru_destroy(struct list_lru *lru);
 int __list_lru_init(struct list_lru *lru, bool memcg_aware,
-		    struct lock_class_key *key, struct shrinker *shrinker);
+		    struct shrinker *shrinker);
 
 #define list_lru_init(lru)				\
-	__list_lru_init((lru), false, NULL, NULL)
+	__list_lru_init((lru), false, NULL)
 #define list_lru_init_memcg(lru, shrinker)		\
-	__list_lru_init((lru), true, NULL, shrinker)
+	__list_lru_init((lru), true, shrinker)
+
+static inline int list_lru_init_memcg_key(struct list_lru *lru, struct shrinker *shrinker,
+					  struct lock_class_key *key)
+{
+#ifdef CONFIG_LOCKDEP
+	lru->key = key;
+#endif
+	return list_lru_init_memcg(lru, shrinker);
+}
 
 int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
 			 gfp_t gfp);

mm/list_lru.c

@@ -562,8 +562,7 @@ static void memcg_destroy_list_lru(struct list_lru *lru)
 }
 #endif /* CONFIG_MEMCG */
 
-int __list_lru_init(struct list_lru *lru, bool memcg_aware,
-		    struct lock_class_key *key, struct shrinker *shrinker)
+int __list_lru_init(struct list_lru *lru, bool memcg_aware, struct shrinker *shrinker)
 {
 	int i;
 
@@ -583,8 +582,10 @@ int __list_lru_init(struct list_lru *lru, bool memcg_aware,
 
 	for_each_node(i) {
 		spin_lock_init(&lru->node[i].lock);
-		if (key)
-			lockdep_set_class(&lru->node[i].lock, key);
+#ifdef CONFIG_LOCKDEP
+		if (lru->key)
+			lockdep_set_class(&lru->node[i].lock, lru->key);
+#endif
 		init_one_lru(&lru->node[i].lru);
 	}
 

mm/workingset.c

@@ -813,8 +813,8 @@ static int __init workingset_init(void)
 	if (!workingset_shadow_shrinker)
 		goto err;
 
-	ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key,
-			      workingset_shadow_shrinker);
+	ret = list_lru_init_memcg_key(&shadow_nodes, workingset_shadow_shrinker,
+				      &shadow_nodes_key);
 	if (ret)
 		goto err_list_lru;