[PATCH v1 01/26] mm: memcontrol: remove dead code of checking parent memory cgroup

Qi Zheng
2025-10-28T14:02:13Z

From: Muchun Song <songmuchun@bytedance.com>

Since the no-hierarchy mode has been deprecated after the commit:

commit bef8620cd8e0 ("mm: memcg: deprecate the non-hierarchical mode").

As a result, parent_mem_cgroup() will not return NULL except when passing
the root memcg, and the root memcg cannot be offline. Hence, it's safe to
remove the check on the returned value of parent_mem_cgroup(). Remove the
corresponding dead code.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
mm/memcontrol.c | 5 -----
mm/shrinker.c | 6 +-----
2 files changed, 1 insertion(+), 10 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 93f7c76f0ce96..d5257465c9d75 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3339,9 +3339,6 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg)
return;

parent = parent_mem_cgroup(memcg);
- if (!parent)
- parent = root_mem_cgroup;
-
memcg_reparent_list_lrus(memcg, parent);

/*
@@ -3632,8 +3629,6 @@ struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg)
break;
}
memcg = parent_mem_cgroup(memcg);
- if (!memcg)
- memcg = root_mem_cgroup;
}
return memcg;
}
diff --git a/mm/shrinker.c b/mm/shrinker.c
index 4a93fd433689a..e8e092a2f7f41 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -286,14 +286,10 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg)
{
int nid, index, offset;
long nr;
- struct mem_cgroup *parent;
+ struct mem_cgroup *parent = parent_mem_cgroup(memcg);
struct shrinker_info *child_info, *parent_info;
struct shrinker_info_unit *child_unit, *parent_unit;

- parent = parent_mem_cgroup(memcg);
- if (!parent)
- parent = root_mem_cgroup;
-
/* Prevent from concurrent shrinker_info expand */
mutex_lock(&shrinker_mutex);
for_each_node(nid) {
--
2.20.1