Re: [PATCH v5 29/32] mm: memcontrol: prepare for reparenting non-hierarchical stats

[Shakeel Butt]

On Wed, Feb 25, 2026 at 03:53:12PM +0800, Qi Zheng wrote:
> From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> 
> To resolve the dying memcg issue, we need to reparent LRU folios of child
> memcg to its parent memcg. This could cause problems for non-hierarchical
> stats.
> 
> As Yosry Ahmed pointed out:
> 
> ```
> In short, if memory is charged to a dying cgroup at the time of
> reparenting, when the memory gets uncharged the stats updates will occur
> at the parent. This will update both hierarchical and non-hierarchical
> stats of the parent, which would corrupt the parent's non-hierarchical
> stats (because those counters were never incremented when the memory was
> charged).
> ```
> 
> Now we have the following two types of non-hierarchical stats, and they
> are only used in CONFIG_MEMCG_V1:
> 
> a. memcg->vmstats->state_local[i]
> b. pn->lruvec_stats->state_local[i]
> 
> To ensure that these non-hierarchical stats work properly, we need to
> reparent these non-hierarchical stats after reparenting LRU folios. To
> this end, this commit makes the following preparations:
> 
> 1. implement reparent_state_local() to reparent non-hierarchical stats
> 2. make css_killed_work_fn() to be called in rcu work, and implement
>    get_non_dying_memcg_start() and get_non_dying_memcg_end() to avoid race
>    between mod_memcg_state()/mod_memcg_lruvec_state()
>    and reparent_state_local()
> 3. change these non-hierarchical stats to atomic_long_t type to avoid race
>    between mem_cgroup_stat_aggregate() and reparent_state_local()
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>

[...]

> --- a/mm/memcontrol-v1.h
> +++ b/mm/memcontrol-v1.h
> @@ -45,6 +45,7 @@ static inline bool do_memsw_account(void)
>  
>  unsigned long memcg_events_local(struct mem_cgroup *memcg, int event);
>  unsigned long memcg_page_state_local(struct mem_cgroup *memcg, int idx);
> +void mod_memcg_page_state_local(struct mem_cgroup *memcg, int idx, unsigned long val);

The above seems like addition by mistake.

After fixing this, you can add:

Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>