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

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Message-ID: <8aee44f5-11ec-410a-9b45-5cb224e9e23a@linux.dev>
Date: Thu, 18 Dec 2025 15:09:04 +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>,
 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 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.