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

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Message-ID: <ab6edd99-30a3-486c-bc47-ffcac3d93b51@linux.dev>
Date: Mon, 13 Oct 2025 15:29:11 +0800
From: Qi Zheng <qi.zheng@...ux.dev>
To: Shakeel Butt <shakeel.butt@...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

Hi Shakeel,

On 10/8/25 1:56 AM, Shakeel Butt wrote:
> 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

OK, will do.

> 
> With that, please add:
> 
> Acked-by: Shakeel Butt <shakeel.butt@...ux.dev>

Thanks!

>