From 5e3bd0c75c61a1a77c7f04f2d16696db9a245477 Mon Sep 17 00:00:00 2001
From: Xueyuan Chen <xueyuan.chen21@gmail.com>
Date: Sun, 30 Aug 2026 12:29:20 +0800
Subject: [PATCH] mm/shmem: split large folios only on -E2BIG

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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>
---
 mm/shmem.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index d3f24b5977bd..84f0a2eb85fe 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1813,7 +1813,7 @@ int shmem_writeout(struct swap_io_ctx *ctx, struct folio *folio,
 	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 @@ int shmem_writeout(struct swap_io_ctx *ctx, struct folio *folio,
 		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 @@ int shmem_writeout(struct swap_io_ctx *ctx, struct folio *folio,
 		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);