Re: [PATCH v3 28/30 fix 1/2] mm: memcontrol: fix lruvec_stats->state_local reparenting

[Muchun Song <muchun.song@linux.dev>]

> On Jan 19, 2026, at 11:36, Qi Zheng <qi.zheng@linux.dev> wrote:
> 
> 
> 
> On 1/18/26 11:22 AM, Shakeel Butt wrote:
>> On Thu, Jan 15, 2026 at 06:41:38PM +0800, Qi Zheng wrote:
>>> From: Qi Zheng <zhengqi.arch@bytedance.com>
>>> 
>>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>>> ---
>>>  include/linux/memcontrol.h |  2 --
>>>  mm/memcontrol-v1.c         |  8 --------
>>>  mm/memcontrol-v1.h         |  5 ++++-
>>>  mm/memcontrol.c            | 19 ++++++++-----------
>>>  4 files changed, 12 insertions(+), 22 deletions(-)
>>> 
>>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>>> index 1fe554eec1e25..e0b84b109b7ac 100644
>>> --- a/include/linux/memcontrol.h
>>> +++ b/include/linux/memcontrol.h
>>> @@ -944,8 +944,6 @@ bool memcg_vm_event_item_valid(enum vm_event_item idx);
>>>  unsigned long lruvec_page_state(struct lruvec *lruvec, enum node_stat_item idx);
>>>  unsigned long lruvec_page_state_local(struct lruvec *lruvec,
>>>         enum node_stat_item idx);
>>> -void reparent_memcg_lruvec_state_local(struct mem_cgroup *memcg,
>>> -        struct mem_cgroup *parent, int idx);
>>>    void mem_cgroup_flush_stats(struct mem_cgroup *memcg);
>>>  void mem_cgroup_flush_stats_ratelimited(struct mem_cgroup *memcg);
>>> diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c
>>> index 03b924920d6a5..daf9bad8c45ea 100644
>>> --- a/mm/memcontrol-v1.c
>>> +++ b/mm/memcontrol-v1.c
>>> @@ -1909,14 +1909,6 @@ void reparent_memcg1_state_local(struct mem_cgroup *memcg, struct mem_cgroup *pa
>>>   reparent_memcg_state_local(memcg, parent, memcg1_stats[i]);
>>>  }
>>>  -void reparent_memcg1_lruvec_state_local(struct mem_cgroup *memcg, struct mem_cgroup *parent)
>>> -{
>>> - int i;
>>> -
>>> - for (i = 0; i < ARRAY_SIZE(memcg1_stats); i++)
>>> - reparent_memcg_lruvec_state_local(memcg, parent, memcg1_stats[i]);
>>> -}
>>> -
>>>  void memcg1_stat_format(struct mem_cgroup *memcg, struct seq_buf *s)
>>>  {
>>>   unsigned long memory, memsw;
>>> diff --git a/mm/memcontrol-v1.h b/mm/memcontrol-v1.h
>>> index 45528195d3578..5b1188f3d4173 100644
>>> --- a/mm/memcontrol-v1.h
>>> +++ b/mm/memcontrol-v1.h
>>> @@ -75,7 +75,6 @@ void memcg1_uncharge_batch(struct mem_cgroup *memcg, unsigned long pgpgout,
>>>    void memcg1_stat_format(struct mem_cgroup *memcg, struct seq_buf *s);
>>>  void reparent_memcg1_state_local(struct mem_cgroup *memcg, struct mem_cgroup *parent);
>>> -void reparent_memcg1_lruvec_state_local(struct mem_cgroup *memcg, struct mem_cgroup *parent);
>>>    void memcg1_account_kmem(struct mem_cgroup *memcg, int nr_pages);
>>>  static inline bool memcg1_tcpmem_active(struct mem_cgroup *memcg)
>>> @@ -116,6 +115,10 @@ static inline void memcg1_uncharge_batch(struct mem_cgroup *memcg,
>>>    static inline void memcg1_stat_format(struct mem_cgroup *memcg, struct seq_buf *s) {}
>>>  +static inline void reparent_memcg1_state_local(struct mem_cgroup *memcg, struct mem_cgroup *parent)
>>> +{
>>> +}
>>> +
>>>  static inline void memcg1_account_kmem(struct mem_cgroup *memcg, int nr_pages) {}
>>>  static inline bool memcg1_tcpmem_active(struct mem_cgroup *memcg) { return false; }
>>>  static inline bool memcg1_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages,
>>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>>> index 7333a37830051..b7b35143d4d2d 100644
>>> --- a/mm/memcontrol.c
>>> +++ b/mm/memcontrol.c
>>> @@ -225,13 +225,13 @@ static inline struct obj_cgroup *__memcg_reparent_objcgs(struct mem_cgroup *memc
>>>   return objcg;
>>>  }
>>>  -#ifdef CONFIG_MEMCG_V1
>>> +static void reparent_memcg_lruvec_state_local(struct mem_cgroup *memcg,
>>> +       struct mem_cgroup *parent, int idx);
>>>  static void __mem_cgroup_flush_stats(struct mem_cgroup *memcg, bool force);
>>>    static inline void reparent_state_local(struct mem_cgroup *memcg, struct mem_cgroup *parent)
>>>  {
>> No reparenting local stats for v2.
> 
> It seems that lruvec_stats->state_local (non-hierarchical) needs to be
> relocated in both v1 and v2.

Here we might need to elaborate a bit. Specifically, in the function
`count_shadow_nodes`, the use of `lruvec_page_state_local` to obtain
LRU and SLAB pages seems to also require these logics to work correctly.
For SLAB, it appears that the statistics here have already been
problematic for a while since SLAB pages have been reparented, right?

> 
>>> - if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
>>> - return;
>>> + int i;
>>>     synchronize_rcu();
>>>  @@ -239,13 +239,10 @@ static inline void reparent_state_local(struct mem_cgroup *memcg, struct mem_cgr
>>>     /* The following counts are all non-hierarchical and need to be reparented. */
>>>   reparent_memcg1_state_local(memcg, parent);
>>> - reparent_memcg1_lruvec_state_local(memcg, parent);
>>> -}
>>> -#else
>>> -static inline void reparent_state_local(struct mem_cgroup *memcg, struct mem_cgroup *parent)
>>> -{
>>> +
>>> + for (i = 0; i < NR_LRU_LISTS; i++)
>>> + reparent_memcg_lruvec_state_local(memcg, parent, i);
>>>  }
>>> -#endif
>>>    static inline void reparent_locks(struct mem_cgroup *memcg, struct mem_cgroup *parent)
>>>  {
>>> @@ -510,8 +507,8 @@ unsigned long lruvec_page_state_local(struct lruvec *lruvec,
>>>   return x;
>>>  }
>>>  -void reparent_memcg_lruvec_state_local(struct mem_cgroup *memcg,
>>> -        struct mem_cgroup *parent, int idx)
>>> +static void reparent_memcg_lruvec_state_local(struct mem_cgroup *memcg,
>>> +       struct mem_cgroup *parent, int idx)
>>>  {
>>>   int i = memcg_stats_index(idx);
>>>   int nid;
>>> -- 
>>> 2.20.1