+ mm-vmscan-allow-writeout-of-swapcache-folios-without-anon-mappings.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: vmscan: allow writeout of swapcache folios without anon mappings
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-vmscan-allow-writeout-of-swapcache-folios-without-anon-mappings.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vmscan-allow-writeout-of-swapcache-folios-without-anon-mappings.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days

------------------------------------------------------
From: Nhat Pham <nphamcs@gmail.com>
Subject: mm: vmscan: allow writeout of swapcache folios without anon mappings
Date: Tue, 10 Nov 2026 07:14:05 -0800

Patch series "mm: fix swapcache writeout and cluster table races", v2.

Reviews of vswap and v1 of this series found bugs in existing swap code. 
Allow swapcache writeout without anon mappings, publish cluster tables
with the allocator locks held, and leave tableless clusters to the
allocator.


This patch (of 3):

Unfaulted zswap readahead folios can be dirty and in swapcache without
an anonymous mapping. pageout() rejects them before swap_writeout(),
so reclaim cannot write them out while their swap entries remain
referenced.

Allow swapcache folios through the filesystem folio check. They already
have swap entries and can use the existing swap writeout path. Anonymous
folios outside swapcache have no mapping and already return PAGE_KEEP.

Link: https://lore.kernel.org/20261110151407.789960-1-nphamcs@gmail.com
Link: https://lore.kernel.org/20261110151407.789960-2-nphamcs@gmail.com
Fixes: 84798514db50 ("mm: Remove swap_writepage() and shmem_writepage()")
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/all/sashiko-outbox-181078@kernel.org/
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Qi Zheng <qi.zheng@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christopher Li <chrisl@kernel.org>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Youngjun Park <youngjun.park@lge.com>
Cc: <ryncsn@gmail.com>
Cc: <stable@vger.kernel.org>
---

 mm/vmscan.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/vmscan.c~mm-vmscan-allow-writeout-of-swapcache-folios-without-anon-mappings
+++ a/mm/vmscan.c
@@ -714,7 +714,8 @@ static pageout_t pageout(struct swap_io_
 	 */
 	if (folio_ref_count(folio) != 1 + folio_nr_pages(folio) || !mapping)
 		return PAGE_KEEP;
-	if (!shmem_mapping(mapping) && !folio_test_anon(folio))
+	/* Anonymous folios outside swapcache returned PAGE_KEEP above. */
+	if (!shmem_mapping(mapping) && !folio_test_swapcache(folio))
 		return PAGE_ACTIVATE;
 	if (!folio_clear_dirty_for_io(folio))
 		return PAGE_CLEAN;
_

Patches currently in -mm which might be from nphamcs@gmail.com are

mm-vmscan-allow-writeout-of-swapcache-folios-without-anon-mappings.patch
mm-swap-publish-cluster-tables-after-reacquiring-allocator-locks.patch
mm-swap-skip-relocation-of-tableless-clusters.patch