linux-kernel - Re: [PATCH v4 30/31] mm: memcontrol: eliminate the problem of dying memory cgroup for LRU folios

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Message-ID: <c921485b-bccc-40b6-b2c7-5163739de9d9@gmail.com>
Date: Sat, 7 Feb 2026 19:59:51 +0000
From: Usama Arif <usamaarif642@...il.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, yosry.ahmed@...ux.dev,
 imran.f.khan@...cle.com, kamalesh.babulal@...cle.com,
 axelrasmussen@...gle.com, yuanchu@...gle.com, weixugc@...gle.com,
 chenridong@...weicloud.com, mkoutny@...e.com, akpm@...ux-foundation.org,
 hamzamahfooz@...ux.microsoft.com, apais@...ux.microsoft.com,
 lance.yang@...ux.dev, bhe@...hat.com
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 v4 30/31] mm: memcontrol: eliminate the problem of dying
 memory cgroup for LRU folios


> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e7d4e4ff411b6..0e0efaa511d3d 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -247,11 +247,25 @@ static inline void reparent_state_local(struct mem_cgroup *memcg, struct mem_cgr
>  
>  static inline void reparent_locks(struct mem_cgroup *memcg, struct mem_cgroup *parent)
>  {
> +	int nid, nest = 0;
> +
>  	spin_lock_irq(&objcg_lock);
> +	for_each_node(nid) {
> +		spin_lock_nested(&mem_cgroup_lruvec(memcg,
> +				 NODE_DATA(nid))->lru_lock, nest++);
> +		spin_lock_nested(&mem_cgroup_lruvec(parent,
> +				 NODE_DATA(nid))->lru_lock, nest++);
> +	}
>  }
>  

mWould this break lockdep on more than 4 NUMA nodes as MAX_LOCKDEP_SUBCLASSES = 8 and
2 locks are being acquired per node.

>  static inline void reparent_unlocks(struct mem_cgroup *memcg, struct mem_cgroup *parent)
>  {
> +	int nid;
> +
> +	for_each_node(nid) {
> +		spin_unlock(&mem_cgroup_lruvec(parent, NODE_DATA(nid))->lru_lock);
> +		spin_unlock(&mem_cgroup_lruvec(memcg, NODE_DATA(nid))->lru_lock);
> +	}
>  	spin_unlock_irq(&objcg_lock);
>  }