linux-kernel - Re: [PATCH v1 13/26] mm: mglru: prevent memory cgroup release in mglru

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Message-ID: <82a16330-f801-46f9-bc4d-b10ae9e1472a@linux.dev>
Date: Thu, 20 Nov 2025 21:39:11 +0800
From: Qi Zheng <qi.zheng@...ux.dev>
To: Harry Yoo <harry.yoo@...cle.com>
Cc: hannes@...xchg.org, hughd@...gle.com, mhocko@...e.com,
 roman.gushchin@...ux.dev, shakeel.butt@...ux.dev, muchun.song@...ux.dev,
 david@...hat.com, lorenzo.stoakes@...cle.com, ziy@...dia.com,
 imran.f.khan@...cle.com, kamalesh.babulal@...cle.com,
 axelrasmussen@...gle.com, yuanchu@...gle.com, weixugc@...gle.com,
 akpm@...ux-foundation.org, 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 v1 13/26] mm: mglru: prevent memory cgroup release in
 mglru



On 11/19/25 6:13 PM, Harry Yoo wrote:
> On Tue, Oct 28, 2025 at 09:58:26PM +0800, 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 mglru.
>>
>> 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>
>> ---
>>   mm/vmscan.c | 23 +++++++++++++++++------
>>   1 file changed, 17 insertions(+), 6 deletions(-)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 660cd40cfddd4..676e6270e5b45 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -4279,6 +4288,8 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
>>   
>>   	arch_leave_lazy_mmu_mode();
>>   
>> +	rcu_read_unlock();
>> +
>>   	/* feedback from rmap walkers to page table walkers */
>>   	if (mm_state && suitable_to_scan(i, young))
>>   		update_bloom_filter(mm_state, max_seq, pvmw->pmd);
> 
> mm_state has the same life cycle as mem_cgroup. So it should be
> protected by rcu read lock?

You are right. The mm_state is defined as follows:

struct lruvec {
         struct lru_gen_mm_state		mm_state;
};

will fix it in the next version.

Thanks,
Qi

>