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

[Qi Zheng]

On 2/26/26 8:25 AM, Shakeel Butt wrote:
> On Wed, Feb 25, 2026 at 06:58:59AM -0800, Yosry Ahmed wrote:
> > > @@ -473,6 +493,29 @@ unsigned long lruvec_page_state_local(struct lruvec *lruvec,
> > >          return x;
> > >   }
> > >
> > > +#ifdef CONFIG_MEMCG_V1
> > > +void reparent_memcg_lruvec_state_local(struct mem_cgroup *memcg,
> > > +                                      struct mem_cgroup *parent, int idx)
> > > +{
> > > +       int i = memcg_stats_index(idx);
> > > +       int nid;
> > > +
> > > +       if (WARN_ONCE(BAD_STAT_IDX(i), "%s: missing stat item %d\n", __func__, idx))
> > > +               return;
> > > +
> > > +       for_each_node(nid) {
> > > +               struct lruvec *child_lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
> > > +               struct lruvec *parent_lruvec = mem_cgroup_lruvec(parent, NODE_DATA(nid));
> > > +               struct mem_cgroup_per_node *parent_pn;
> > > +               unsigned long value = lruvec_page_state_local(child_lruvec, idx);
> > > +
> > > +               parent_pn = container_of(parent_lruvec, struct mem_cgroup_per_node, lruvec);
> > > +
> > > +               atomic_long_add(value, &(parent_pn->lruvec_stats->state_local[i]));
> > > +       }
> > > +}
> >
> > Did you measure the impact of making state_local atomic on the flush
> > path? It's a slow path but we've seen pain from it being too slow
> > before, because it extends the critical section of the rstat flush
> > lock.
>
> Qi, please measure the impact on flushing and if no impact then no need to do

OK, will try to do it.

> anything as I don't want anymore churn in this series.

Agree.

>