linux-kernel - [RFC v2 2/3] huge_memory: skip warning if min order and folio order are same in split

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251206030858.1418814-3-p.raghav@samsung.com>
Date: Sat,  6 Dec 2025 04:08:57 +0100
From: Pankaj Raghav <p.raghav@...sung.com>
To: Suren Baghdasaryan <surenb@...gle.com>,
	Mike Rapoport <rppt@...nel.org>,
	David Hildenbrand <david@...hat.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Michal Hocko <mhocko@...e.com>,
	Lance Yang <lance.yang@...ux.dev>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Dev Jain <dev.jain@....com>,
	Barry Song <baohua@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nico Pache <npache@...hat.com>,
	Zi Yan <ziy@...dia.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	Jens Axboe <axboe@...nel.dk>
Cc: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-block@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	mcgrof@...nel.org,
	gost.dev@...sung.com,
	kernel@...kajraghav.com,
	tytso@....edu,
	Pankaj Raghav <p.raghav@...sung.com>
Subject: [RFC v2 2/3] huge_memory: skip warning if min order and folio order are same in split

When THP is disabled, file-backed large folios max order is capped to the
min order to avoid using the splitting infrastructure.

Currently, splitting calls will create a warning when called with THP
disabled. But splitting call does not have to do anything when min order
is same as the folio order.

So skip the warning in folio split functions if the min order is same as
the folio order for file backed folios.

Due to issues with circular dependency, move the definition of split
function for !CONFIG_TRANSPARENT_HUGEPAGES to mm/memory.c

Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
---
 include/linux/huge_mm.h | 40 ++++++++--------------------------------
 mm/memory.c             | 41 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+), 32 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 21162493a0a0..71e309f2d26a 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -612,42 +612,18 @@ can_split_folio(struct folio *folio, int caller_pins, int *pextra_pins)
 {
 	return false;
 }
-static inline int
-split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
-		unsigned int new_order)
-{
-	VM_WARN_ON_ONCE_PAGE(1, page);
-	return -EINVAL;
-}
-static inline int split_huge_page_to_order(struct page *page, unsigned int new_order)
-{
-	VM_WARN_ON_ONCE_PAGE(1, page);
-	return -EINVAL;
-}
+int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
+		unsigned int new_order);
+int split_huge_page_to_order(struct page *page, unsigned int new_order);
 static inline int split_huge_page(struct page *page)
 {
-	VM_WARN_ON_ONCE_PAGE(1, page);
-	return -EINVAL;
-}
-
-static inline unsigned int min_order_for_split(struct folio *folio)
-{
-	VM_WARN_ON_ONCE_FOLIO(1, folio);
-	return 0;
-}
-
-static inline int split_folio_to_list(struct folio *folio, struct list_head *list)
-{
-	VM_WARN_ON_ONCE_FOLIO(1, folio);
-	return -EINVAL;
+	return split_huge_page_to_list_to_order(page, NULL, 0);
 }
 
-static inline int try_folio_split_to_order(struct folio *folio,
-		struct page *page, unsigned int new_order)
-{
-	VM_WARN_ON_ONCE_FOLIO(1, folio);
-	return -EINVAL;
-}
+unsigned int min_order_for_split(struct folio *folio);
+int split_folio_to_list(struct folio *folio, struct list_head *list);
+int try_folio_split_to_order(struct folio *folio,
+		struct page *page, unsigned int new_order);
 
 static inline void deferred_split_folio(struct folio *folio, bool partially_mapped) {}
 static inline void reparent_deferred_split_queue(struct mem_cgroup *memcg) {}
diff --git a/mm/memory.c b/mm/memory.c
index 6675e87eb7dd..4eccdf72a46e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4020,6 +4020,47 @@ static bool __wp_can_reuse_large_anon_folio(struct folio *folio,
 {
 	BUILD_BUG();
 }
+
+int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
+				     unsigned int new_order)
+{
+	struct folio *folio = page_folio(page);
+	unsigned int order = mapping_min_folio_order(folio->mapping);
+
+	if (!folio_test_anon(folio) && order == folio_order(folio))
+		return -EINVAL;
+
+	VM_WARN_ON_ONCE_PAGE(1, page);
+	return -EINVAL;
+}
+
+int split_huge_page_to_order(struct page *page, unsigned int new_order)
+{
+	return split_huge_page_to_list_to_order(page, NULL, new_order);
+}
+
+int split_folio_to_list(struct folio *folio, struct list_head *list)
+{
+	unsigned int order = mapping_min_folio_order(folio->mapping);
+
+	if (!folio_test_anon(folio) && order == folio_order(folio))
+		return -EINVAL;
+
+	VM_WARN_ON_ONCE_FOLIO(1, folio);
+	return -EINVAL;
+}
+
+unsigned int min_order_for_split(struct folio *folio)
+{
+	return split_folio_to_list(folio, NULL);
+}
+
+
+int try_folio_split_to_order(struct folio *folio, struct page *page,
+			     unsigned int new_order)
+{
+	return split_folio_to_list(folio, NULL);
+}
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
 static bool wp_can_reuse_anon_folio(struct folio *folio,
-- 
2.50.1