linux-kernel - Re: [PATCH v2 11/28] mm: memcontrol: prevent memory cgroup release in count_memcg_folio

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Message-ID: <8354b8b7-2d94-431b-b60a-6a744ab7ca06@huaweicloud.com>
Date: Fri, 26 Dec 2025 10:12:01 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Qi Zheng <qi.zheng@...ux.dev>, hannes@...xchg.org, hughd@...gle.com,
 mhocko@...e.com, roman.gushchin@...ux.dev, shakeel.butt@...ux.dev,
 muchun.song@...ux.dev, david@...nel.org, lorenzo.stoakes@...cle.com,
 ziy@...dia.com, harry.yoo@...cle.com, imran.f.khan@...cle.com,
 kamalesh.babulal@...cle.com, axelrasmussen@...gle.com, yuanchu@...gle.com,
 weixugc@...gle.com, mkoutny@...e.com, akpm@...ux-foundation.org,
 hamzamahfooz@...ux.microsoft.com, apais@...ux.microsoft.com,
 lance.yang@...ux.dev
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 cgroups@...r.kernel.org, Muchun Song <songmuchun@...edance.com>,
 Qi Zheng <zhengqi.arch@...edance.com>
Subject: Re: [PATCH v2 11/28] mm: memcontrol: prevent memory cgroup release in
 count_memcg_folio_events()



On 2025/12/17 15:27, Qi Zheng wrote:
> From: Muchun Song <songmuchun@...edance.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@...edance.com>
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> Reviewed-by: Harry Yoo <harry.yoo@...cle.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@...wei.com>

-- 
Best regards,
Ridong