+ mm-shmem-split-large-folios-only-on-e2big.patch added to mm-new branch

+ mm-shmem-split-large-folios-only-on-e2big.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/shmem: split large folios only on -E2BIG
has been added to the -mm mm-new branch.  Its filename is
     mm-shmem-split-large-folios-only-on-e2big.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-shmem-split-large-folios-only-on-e2big.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: Xueyuan Chen <xueyuan.chen21@gmail.com>
Subject: mm/shmem: split large folios only on -E2BIG
Date: Sun, 30 Aug 2026 12:29:20 +0800

shmem_writeout() currently splits a large folio on every
folio_alloc_swap() failure.  With the refined return-value contract, only
-E2BIG indicates that splitting might allow smaller folios to be swapped
out.

Enter the split fallback only for -E2BIG.  For -ENOSPC and -ENOMEM,
redirty and reactivate the folio as before.

Link: https://lore.kernel.org/20260830042920.2280454-5-xueyuan.chen21@gmail.com
Signed-off-by: Xueyuan Chen <xueyuan.chen21@gmail.com>
Suggested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Barry Song <baohua@kernel.org>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Chris Li <chrisl@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nanzhe Zhao <zhaonanzhe@xiaomi.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Youngjun Park <youngjun.park@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/shmem.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/mm/shmem.c~mm-shmem-split-large-folios-only-on-e2big
+++ a/mm/shmem.c
@@ -1813,7 +1813,7 @@ int shmem_writeout(struct swap_io_ctx *c
 	struct shmem_inode_info *info = SHMEM_I(inode);
 	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
 	pgoff_t index;
-	int nr_pages;
+	int nr_pages, ret;
 	bool split = false;
 
 	if ((info->flags & SHMEM_F_LOCKED) || sbinfo->noswap)
@@ -1894,7 +1894,8 @@ try_split:
 		folio_mark_uptodate(folio);
 	}
 
-	if (!folio_alloc_swap(folio)) {
+	ret = folio_alloc_swap(folio);
+	if (!ret) {
 		bool first_swapped = shmem_recalc_inode(inode, 0, nr_pages);
 		int error;
 
@@ -1947,7 +1948,7 @@ try_split:
 		swap_cache_del_folio(folio);
 		goto redirty;
 	}
-	if (nr_pages > 1)
+	if (nr_pages > 1 && ret == -E2BIG)
 		goto try_split;
 redirty:
 	folio_mark_dirty(folio);
_

Patches currently in -mm which might be from xueyuan.chen21@gmail.com are

mm-distinguish-large-folio-swap-allocation-failures.patch
mm-shmem-split-large-folios-only-on-e2big.patch