linux-kernel - [PATCH v1 24/26] mm: memcontrol: refactor memcg_reparent

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Message-ID: <21f6b42ec2441372bdfb540d2e7e0fef770c0f6c.1761658311.git.zhengqi.arch@bytedance.com>
Date: Tue, 28 Oct 2025 21:58:37 +0800
From: Qi Zheng <qi.zheng@...ux.dev>
To: hannes@...xchg.org,
	hughd@...gle.com,
	mhocko@...e.com,
	roman.gushchin@...ux.dev,
	shakeel.butt@...ux.dev,
	muchun.song@...ux.dev,
	david@...hat.com,
	lorenzo.stoakes@...cle.com,
	ziy@...dia.com,
	harry.yoo@...cle.com,
	imran.f.khan@...cle.com,
	kamalesh.babulal@...cle.com,
	axelrasmussen@...gle.com,
	yuanchu@...gle.com,
	weixugc@...gle.com,
	akpm@...ux-foundation.org
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org,
	Qi Zheng <zhengqi.arch@...edance.com>
Subject: [PATCH v1 24/26] 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>
---
 mm/memcontrol.c | 37 +++++++++++++++++++++++++++----------
 mm/vmscan.c     |  1 -
 2 files changed, 27 insertions(+), 11 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7969dd93d858a..ee98c9e8fdcea 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -206,24 +206,41 @@ static struct obj_cgroup *obj_cgroup_alloc(void)
 	return objcg;
 }
 
-static void memcg_reparent_objcgs(struct mem_cgroup *memcg)
+static void __memcg_reparent_objcgs(struct mem_cgroup *src,
+				    struct mem_cgroup *dst)
 {
 	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);
 
+	objcg = rcu_replace_pointer(src->objcg, NULL, true);
 	/* 1) Ready to reparent active objcg. */
-	list_add(&objcg->list, &memcg->objcg_list);
+	list_add(&objcg->list, &src->objcg_list);
 	/* 2) Reparent active objcg and already reparented objcgs to parent. */
-	list_for_each_entry(iter, &memcg->objcg_list, list)
-		WRITE_ONCE(iter->memcg, parent);
+	list_for_each_entry(iter, &src->objcg_list, list)
+		WRITE_ONCE(iter->memcg, dst);
 	/* 3) Move already reparented objcgs to the parent's list */
-	list_splice(&memcg->objcg_list, &parent->objcg_list);
+	list_splice(&src->objcg_list, &dst->objcg_list);
+}
+
+static void reparent_locks(struct mem_cgroup *src, struct mem_cgroup *dst)
+{
+	spin_lock_irq(&objcg_lock);
+}
 
+static void reparent_unlocks(struct mem_cgroup *src, struct mem_cgroup *dst)
+{
 	spin_unlock_irq(&objcg_lock);
+}
+
+static void memcg_reparent_objcgs(struct mem_cgroup *src)
+{
+	struct obj_cgroup *objcg = rcu_dereference_protected(src->objcg, true);
+	struct mem_cgroup *dst = parent_mem_cgroup(src);
+
+	reparent_locks(src, dst);
+
+	__memcg_reparent_objcgs(src, dst);
+
+	reparent_unlocks(src, dst);
 
 	percpu_ref_kill(&objcg->refcnt);
 }
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3ee7fb96b8aeb..82c4cc6edbca5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2649,7 +2649,6 @@ static bool can_age_anon_pages(struct lruvec *lruvec,
 			  lruvec_memcg(lruvec));
 }
 
-
 #ifdef CONFIG_MEMCG
 static void lruvec_reparent_lru(struct lruvec *src, struct lruvec *dst,
 				enum lru_list lru)
-- 
2.20.1