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

[Qi Zheng]

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.