On 2025/12/17 15:27, Qi Zheng wrote:
> From: Muchun Song <songmuchun@bytedance.com>
>
> In the near future, a folio will no longer pin its corresponding
> memory cgroup. To ensure safety, it will only be appropriate to
> hold the rcu read lock or acquire a reference to the memory cgroup
> returned by folio_memcg(), thereby preventing it from being released.
>
> In the current patch, the rcu read lock is employed to safeguard
> against the release of the memory cgroup in count_memcg_folio_events().
>
> This serves as a preparatory measure for the reparenting of the
> LRU pages.
>
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
> ---
> include/linux/memcontrol.h | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index bc526e0d37e0b..69c4bcfb3c3cd 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -974,10 +974,15 @@ void count_memcg_events(struct mem_cgroup *memcg, enum vm_event_item idx,
> static inline void count_memcg_folio_events(struct folio *folio,
> enum vm_event_item idx, unsigned long nr)
> {
> - struct mem_cgroup *memcg = folio_memcg(folio);
> + struct mem_cgroup *memcg;
>
> - if (memcg)
> - count_memcg_events(memcg, idx, nr);
> + if (!folio_memcg_charged(folio))
> + return;
> +
> + rcu_read_lock();
> + memcg = folio_memcg(folio);
> + count_memcg_events(memcg, idx, nr);
> + rcu_read_unlock();
> }
>
> static inline void count_memcg_events_mm(struct mm_struct *mm,
Reviewed-by: Chen Ridong <chenridong@huawei.com>
--
Best regards,
Ridong