linux-kernel - Re: [PATCH v2 20/28] mm: zswap: prevent lruvec release in zswap_folio

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Message-ID: <aUP7VkCmTVSoMdBN@cmpxchg.org>
Date: Thu, 18 Dec 2025 08:02:14 -0500
From: Johannes Weiner <hannes@...xchg.org>
To: Qi Zheng <qi.zheng@...ux.dev>
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>,
	Nhat Pham <nphamcs@...il.com>,
	Chengming Zhou <chengming.zhou@...ux.dev>,
	Qi Zheng <zhengqi.arch@...edance.com>
Subject: Re: [PATCH v2 20/28] mm: zswap: prevent lruvec release in
 zswap_folio_swapin()

On Thu, Dec 18, 2025 at 03:09:04PM +0800, Qi Zheng wrote:
> 
> 
> 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@...edance.com>
> >>
> >> 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@...edance.com>
> >> Acked-by: Nhat Pham <nphamcs@...il.com>
> >> Reviewed-by: Chengming Zhou <chengming.zhou@...ux.dev>
> >> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> >> Reviewed-by: Harry Yoo <harry.yoo@...cle.com>
> > 
> > Acked-by: Johannes Weiner <hannes@...xchg.org>
> 
> 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.

Ok, that works for me!