Re: [PATCH v2 20/28] mm: zswap: prevent lruvec release in zswap_folio_swapin()

[Qi Zheng]

On 12/18/25 6:33 AM, Johannes Weiner wrote:
> On Wed, Dec 17, 2025 at 03:27:44PM +0800, Qi Zheng wrote:
> > From: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> >
> > In the near future, a folio will no longer pin its corresponding
> > memory cgroup. So an lruvec returned by folio_lruvec() could be
> > released without the rcu read lock or a reference to its memory
> > cgroup.
> >
> > In the current patch, the rcu read lock is employed to safeguard
> > against the release of the lruvec in zswap_folio_swapin().
> >
> > This serves as a preparatory measure for the reparenting of the
> > LRU pages.
> >
> > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> > Acked-by: Nhat Pham <nphamcs@xxxxxxxxx>
> > Reviewed-by: Chengming Zhou <chengming.zhou@xxxxxxxxx>
> > Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> > Reviewed-by: Harry Yoo <harry.yoo@xxxxxxxxxx>
>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Thanks!

> Btw, it would make the series shorter if you combined the changes to
> workingset.c, zswap.c etc. It should still be easy to review as long
> as you just stick to making folio_memcg(), folio_lruvec() calls safe.

I prefer to separate them. For example, as you pointed out, in some
places, it would be more appropriate to switch to use
get_mem_cgroup_from_folio() to handle it. Separating them also makes
subsequent updates and iterations easier.