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

[Johannes Weiner]

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. Maybe do a get and a
put instead?