[PATCH v4 27/31] mm: memcontrol: refactor memcg_reparent_objcgs()

[Qi Zheng <qi.zheng@linux.dev>]

From: Qi Zheng <zhengqi.arch@bytedance.com>

Refactor the memcg_reparent_objcgs() to facilitate subsequent reparenting
LRU folios here.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
---
 mm/memcontrol.c | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 115a1f34bcef9..c9b5dfd822d0a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -208,15 +208,12 @@ static struct obj_cgroup *obj_cgroup_alloc(void)
 	return objcg;
 }
 
-static void memcg_reparent_objcgs(struct mem_cgroup *memcg)
+static inline struct obj_cgroup *__memcg_reparent_objcgs(struct mem_cgroup *memcg,
+							 struct mem_cgroup *parent)
 {
 	struct obj_cgroup *objcg, *iter;
-	struct mem_cgroup *parent = parent_mem_cgroup(memcg);
 
 	objcg = rcu_replace_pointer(memcg->objcg, NULL, true);
-
-	spin_lock_irq(&objcg_lock);
-
 	/* 1) Ready to reparent active objcg. */
 	list_add(&objcg->list, &memcg->objcg_list);
 	/* 2) Reparent active objcg and already reparented objcgs to parent. */
@@ -225,7 +222,29 @@ static void memcg_reparent_objcgs(struct mem_cgroup *memcg)
 	/* 3) Move already reparented objcgs to the parent's list */
 	list_splice(&memcg->objcg_list, &parent->objcg_list);
 
+	return objcg;
+}
+
+static inline void reparent_locks(struct mem_cgroup *memcg, struct mem_cgroup *parent)
+{
+	spin_lock_irq(&objcg_lock);
+}
+
+static inline void reparent_unlocks(struct mem_cgroup *memcg, struct mem_cgroup *parent)
+{
 	spin_unlock_irq(&objcg_lock);
+}
+
+static void memcg_reparent_objcgs(struct mem_cgroup *memcg)
+{
+	struct obj_cgroup *objcg;
+	struct mem_cgroup *parent = parent_mem_cgroup(memcg);
+
+	reparent_locks(memcg, parent);
+
+	objcg = __memcg_reparent_objcgs(memcg, parent);
+
+	reparent_unlocks(memcg, parent);
 
 	percpu_ref_kill(&objcg->refcnt);
 }
-- 
2.20.1