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Date: Thu, 20 Aug 2026 16:38:13 +0100
From: Matthew Wilcox <willy@infradead.org>
To: Barry Song <baohua@kernel.org>
Cc: Alexandre Ghiti <alex@ghiti.fr>, Johannes Weiner <hannes@cmpxchg.org>,
	Yosry Ahmed <yosry@kernel.org>, Nhat Pham <nphamcs@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Chris Li <chrisl@kernel.org>, Kairui Song <kasong@tencent.com>,
	Kairui Song <ryncsn@gmail.com>,
	Chengming Zhou <chengming.zhou@linux.dev>, Jan Kara <jack@suse.cz>,
	Kemeng Shi <shikemeng@huaweicloud.com>,
	Baoquan He <baoquan.he@linux.dev>,
	Youngjun Park <youngjun.park@lge.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christian Brauner <brauner@kernel.org>,
	David Hildenbrand <david@kernel.org>,
	Lorenzo Stoakes <ljs@kernel.org>, Michal Hocko <mhocko@kernel.org>,
	Axel Rasmussen <axelrasmussen@google.com>,
	Qi Zheng <qi.zheng@linux.dev>,
	Shakeel Butt <shakeel.butt@linux.dev>, Wei Xu <weixugc@google.com>,
	Yuanchu Xie <yuanchu@google.com>, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v3 2/3] mm: swap: drop dropbehind swap cache folios on
 writeback completion
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References: <20260818163221.589352-1-alex@ghiti.fr>
 <20260818163221.589352-3-alex@ghiti.fr>
 <CAGsJ_4zC+wAuevG+i5y23rLPGXn0P=D7JpMECnZ1OuP1BsyYkw@mail.gmail.com>
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On Thu, Aug 20, 2026 at 07:36:42PM +0800, Barry Song wrote:
> > +void swap_writeback_dropbehind_folio(struct folio *folio)
> > +{
> > +       llist_add((struct llist_node *)&folio->lru,
> > +                 raw_cpu_ptr(&swap_dropbehind_llist));
> > +       queue_work(swap_dropbehind_wq, &swap_dropbehind_work);
> > +}
> > +
> 
> This is good. For file dropbehind, I see both F2FS [1] and block
> devices [2] reinventing workqueues in their own filesystems or
> drivers, while folio_end_dropbehind() simply benefits from its safe,
> sleepable context. This seems a bit odd.
> 
> So I'm really curious whether this could be extended to file-backed
> folios as well, so that those filesystems and device drivers don't
> have to deal with this themselves.

You should probably both be aware of Tal's series:

https://lore.kernel.org/linux-mm/20260730-blk-dontcache-v7-0-3e8e6850068d@columbia.edu/

In fact, I'd base this series on Tal's.  It would be considerably
easier.