linux-kernel - Re: [PATCH v4 4/4] mm: thp: reparent the split queue during memcg offline

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Message-ID: <sdpkprxqf43emy5sttfzxnv4aemlarimdybdva4xyywyndajtx@zyvckuxgujzm>
Date: Tue, 7 Oct 2025 10:56:54 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Qi Zheng <qi.zheng@...ux.dev>
Cc: hannes@...xchg.org, hughd@...gle.com, mhocko@...e.com, 
	roman.gushchin@...ux.dev, muchun.song@...ux.dev, david@...hat.com, 
	lorenzo.stoakes@...cle.com, ziy@...dia.com, harry.yoo@...cle.com, 
	baolin.wang@...ux.alibaba.com, Liam.Howlett@...cle.com, npache@...hat.com, ryan.roberts@....com, 
	dev.jain@....com, baohua@...nel.org, lance.yang@...ux.dev, 
	akpm@...ux-foundation.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	cgroups@...r.kernel.org, Qi Zheng <zhengqi.arch@...edance.com>
Subject: Re: [PATCH v4 4/4] mm: thp: reparent the split queue during memcg
 offline

On Sat, Oct 04, 2025 at 12:53:18AM +0800, Qi Zheng wrote:
> From: Qi Zheng <zhengqi.arch@...edance.com>
> 
> Similar to list_lru, the split queue is relatively independent and does
> not need to be reparented along with objcg and LRU folios (holding
> objcg lock and lru lock). So let's apply the similar mechanism as list_lru
> to reparent the split queue separately when memcg is offine.
> 
> This is also a preparation for reparenting LRU folios.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> ---
>  include/linux/huge_mm.h |  4 +++
>  mm/huge_memory.c        | 54 +++++++++++++++++++++++++++++++++++++++++
>  mm/memcontrol.c         |  1 +
>  3 files changed, 59 insertions(+)
> 
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index f327d62fc9852..0c211dcbb0ec1 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -417,6 +417,9 @@ static inline int split_huge_page(struct page *page)
>  	return split_huge_page_to_list_to_order(page, NULL, ret);
>  }
>  void deferred_split_folio(struct folio *folio, bool partially_mapped);
> +#ifdef CONFIG_MEMCG
> +void reparent_deferred_split_queue(struct mem_cgroup *memcg);
> +#endif
>  
>  void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>  		unsigned long address, bool freeze);
> @@ -611,6 +614,7 @@ static inline int try_folio_split(struct folio *folio, struct page *page,
>  }
>  
>  static inline void deferred_split_folio(struct folio *folio, bool partially_mapped) {}
> +static inline void reparent_deferred_split_queue(struct mem_cgroup *memcg) {}
>  #define split_huge_pmd(__vma, __pmd, __address)	\
>  	do { } while (0)
>  
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 59ddebc9f3232..b5eea2091cdf6 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1099,6 +1099,11 @@ static struct deferred_split *memcg_split_queue(int nid, struct mem_cgroup *memc
>  {
>  	return memcg ? &memcg->deferred_split_queue : split_queue_node(nid);
>  }
> +
> +static bool memcg_is_dying(struct mem_cgroup *memcg)
> +{
> +	return memcg ? css_is_dying(&memcg->css) : false;
> +}

Please move the above function to include/linux/memcontrol.h

With that, please add:

Acked-by: Shakeel Butt <shakeel.butt@...ux.dev>