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

[Qi Zheng <qi.zheng@linux.dev>]

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.

>