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

[Qi Zheng]

On 2/26/26 9:41 AM, Shakeel Butt wrote:
> 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.

Yes, my mistake, need to be deleted directly. ;)

> After fixing this, you can add:
>
> Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>

Thanks!

>