linux-kernel - [PATCH] mm/huge_memory: fix folio split check for anon folios in swapcache.

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Message-ID: <20251105162910.752266-1-ziy@nvidia.com>
Date: Wed,  5 Nov 2025 11:29:10 -0500
From: Zi Yan <ziy@...dia.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...nel.org>,
	Wei Yang <richard.weiyang@...il.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Zi Yan <ziy@...dia.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Nico Pache <npache@...hat.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Dev Jain <dev.jain@....com>,
	Barry Song <baohua@...nel.org>,
	Lance Yang <lance.yang@...ux.dev>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: [PATCH] mm/huge_memory: fix folio split check for anon folios in swapcache.

Both uniform and non uniform split check missed the check to prevent
splitting anon folios in swapcache to non-zero order. Fix the check.

Fixes: 58729c04cf10 ("mm/huge_memory: add buddy allocator like (non-uniform) folio_split()")
Reported-by: "David Hildenbrand (Red Hat)" <david@...nel.org>
Closes: https://lore.kernel.org/all/dc0ecc2c-4089-484f-917f-920fdca4c898@kernel.org/
Cc: stable@...r.kernel.org
Signed-off-by: Zi Yan <ziy@...dia.com>
---
 mm/huge_memory.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 36fc4ff002c9..595811c78f42 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3674,7 +3674,8 @@ bool non_uniform_split_supported(struct folio *folio, unsigned int new_order,
 		/* order-1 is not supported for anonymous THP. */
 		VM_WARN_ONCE(warns && new_order == 1,
 				"Cannot split to order-1 folio");
-		return new_order != 1;
+		if (new_order == 1)
+			return false;
 	} else if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
 	    !mapping_large_folio_support(folio->mapping)) {
 		/*
@@ -3705,7 +3706,8 @@ bool uniform_split_supported(struct folio *folio, unsigned int new_order,
 	if (folio_test_anon(folio)) {
 		VM_WARN_ONCE(warns && new_order == 1,
 				"Cannot split to order-1 folio");
-		return new_order != 1;
+		if (new_order == 1)
+			return false;
 	} else  if (new_order) {
 		if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
 		    !mapping_large_folio_support(folio->mapping)) {
-- 
2.51.0