+ mm-swap-revert-to-single-folio-writes-for-synchronous-swap-devices.patch added to mm-new branch

+ mm-swap-revert-to-single-folio-writes-for-synchronous-swap-devices.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/swap: revert to single-folio writes for synchronous swap devices
has been added to the -mm mm-new branch.  Its filename is
     mm-swap-revert-to-single-folio-writes-for-synchronous-swap-devices.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swap-revert-to-single-folio-writes-for-synchronous-swap-devices.patch

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

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Christoph Hellwig <hch@lst.de>
Subject: mm/swap: revert to single-folio writes for synchronous swap devices
Date: Thu, 23 Jul 2026 07:46:04 +0200

Patch series "swap_ops updates", v2.

This series is a follow on to the swap ops series now in mm-unstable.

The first patch reintroduces direct folio writes for synchronous
swap files, the other two remove the double indirect for file
system based swap.


This patch (of 3):

Kairui Song reported that zram benefits from submitting each folio
directly instead of batching up I/O because the classic LRU scanning
benefits from clearing the folio writeback bit in the scan loop.

Accommodate that by kicking off writes for synchronous devices for each
iteration.

Link: https://lore.kernel.org/20260723054622.3460249-1-hch@lst.de
Link: https://lore.kernel.org/20260723054622.3460249-2-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Usama Arif <usama.arif@linux.dev>
Acked-by: Chris Li <chrisl@kernel.org>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Steve French <sfrench@samba.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_io.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

--- a/mm/page_io.c~mm-swap-revert-to-single-folio-writes-for-synchronous-swap-devices
+++ a/mm/page_io.c
@@ -358,7 +358,16 @@ static void swap_add_folio(struct swap_i
 	}
 	bvec_set_folio(&sio->bvecs[sio->nr_bvecs], folio, folio_size(folio), 0);
 	sio->len += folio_size(folio);
-	if (++sio->nr_bvecs == ARRAY_SIZE(sio->bvecs)) {
+
+	/*
+	 * Write out the iocb if we filled it, or if the device is synchronous.
+	 *
+	 * The latter is to work around expectations in the classic LRU code
+	 * which make synchronous clearing of the folio writeback flag in the
+	 * reclaim path beneficial.
+	 */
+	if (++sio->nr_bvecs == ARRAY_SIZE(sio->bvecs) ||
+	    (rw == WRITE && (sis->flags & SWP_SYNCHRONOUS_IO))) {
 		if (rw == WRITE)
 			swap_write_submit(ctx);
 		else
_

Patches currently in -mm which might be from hch@lst.de are

shmem-provide-a-shmem_write_folio-wrapper.patch
mm-swap-introduce-struct-swap_io_ctx.patch
mm-swap-also-use-struct-swap_iocb-for-block-i-o.patch
mm-swap-remove-count_swpout_vm_event.patch
mm-swap-use-swap_ops-to-register-swap-devices-methods.patch
mm-swap-remove-swp_fs_ops.patch
mm-vmstat-add-nrswpinout-counters.patch
mm-swap-revert-to-single-folio-writes-for-synchronous-swap-devices.patch
mm-swap-add-a-new-swap_opsh-header-to-allow-for-pluggable-swap-ops.patch
mm-swap-move-swap_ops-into-file-systems-for-file-system-based-swap.patch