linux-kernel - Re: [PATCH v2 14/28] mm: mglru: prevent memory cgroup release in mglru

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Message-ID: <4513ee04-03ff-4de0-bbf4-b5b35dfd41ad@linux.dev>
Date: Thu, 18 Dec 2025 14:50:19 +0800
From: Qi Zheng <qi.zheng@...ux.dev>
To: Johannes Weiner <hannes@...xchg.org>
Cc: 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,
 chenridong@...weicloud.com, mkoutny@...e.com, akpm@...ux-foundation.org,
 hamzamahfooz@...ux.microsoft.com, apais@...ux.microsoft.com,
 lance.yang@...ux.dev, 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 14/28] mm: mglru: prevent memory cgroup release in
 mglru



On 12/18/25 6:18 AM, Johannes Weiner wrote:
> On Wed, Dec 17, 2025 at 03:27:38PM +0800, Qi Zheng wrote:
>> @@ -4242,6 +4244,13 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
>>   		}
>>   	}
>>   
>> +	rcu_read_lock();
>> +	memcg = folio_memcg(folio);
>> +	lruvec = mem_cgroup_lruvec(memcg, pgdat);
>> +	max_seq = READ_ONCE((lruvec)->lrugen.max_seq);
>> +	gen = lru_gen_from_seq(max_seq);
>> +	mm_state = get_mm_state(lruvec);
>> +
>>   	arch_enter_lazy_mmu_mode();
>>   
>>   	pte -= (addr - start) / PAGE_SIZE;
>> @@ -4282,6 +4291,8 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
>>   	if (mm_state && suitable_to_scan(i, young))
>>   		update_bloom_filter(mm_state, max_seq, pvmw->pmd);
>>   
>> +	rcu_read_unlock();
>> +
>>   	return true;
> 
> This seems a bit long to be holding the rcu lock. 

Indeed.

> Maybe do a get and a
> put instead?

OK, will use get_mem_cgroup_from_folio(folio) to do this.

This way, #8 doesn't need to be folded into #27.