linux-kernel - [PATCH v3 27/30] mm: memcontrol: refactor memcg_reparent

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Message-ID: <843e9537bf6b99cc7f19744a6f53b92338c96bfe.1768389889.git.zhengqi.arch@bytedance.com>
Date: Wed, 14 Jan 2026 19:32:54 +0800
From: Qi Zheng <qi.zheng@...ux.dev>
To: hannes@...xchg.org,
	hughd@...gle.com,
	mhocko@...e.com,
	roman.gushchin@...ux.dev,
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Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org,
	Qi Zheng <zhengqi.arch@...edance.com>
Subject: [PATCH v3 27/30] mm: memcontrol: refactor memcg_reparent_objcgs()

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

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

Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
Acked-by: Johannes Weiner <hannes@...xchg.org>
---
 mm/memcontrol.c | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a1573600d4188..70583394f421f 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