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Message-ID: <20251126035008.1919461-2-ziy@nvidia.com>
Date: Tue, 25 Nov 2025 22:50:05 -0500
From: Zi Yan <ziy@...dia.com>
To: David Hildenbrand <david@...nel.org>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
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>,
Miaohe Lin <linmiaohe@...wei.com>,
Naoya Horiguchi <nao.horiguchi@...il.com>,
Wei Yang <richard.weiyang@...il.com>,
Balbir Singh <balbirs@...dia.com>,
linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: [PATCH v3 1/4] mm/huge_memory: change folio_split_supported() to folio_check_splittable()
folio_split_supported() used in try_folio_split_to_order() requires
folio->mapping to be non NULL, but current try_folio_split_to_order() does
not check it. There is no issue in the current code, since
try_folio_split_to_order() is only used in truncate_inode_partial_folio(),
where folio->mapping is not NULL.
To prevent future misuse, move folio->mapping NULL check (i.e., folio is
truncated) into folio_split_supported(). Since folio->mapping NULL check
returns -EBUSY and folio_split_supported() == false means -EINVAL, change
folio_split_supported() return type from bool to int and return error
numbers accordingly. Rename folio_split_supported() to
folio_check_splittable() to match the return type change.
While at it, move is_huge_zero_folio() check and folio_test_writeback()
check into folio_check_splittable() and add kernel-doc.
Remove all warnings inside folio_check_splittable() and give warnings
in __folio_split() instead, so that bool warns parameter can be removed.
Signed-off-by: Zi Yan <ziy@...dia.com>
Reviewed-by: Wei Yang <richard.weiyang@...il.com>
---
include/linux/huge_mm.h | 6 ++--
mm/huge_memory.c | 76 +++++++++++++++++++++++------------------
2 files changed, 46 insertions(+), 36 deletions(-)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 1d439de1ca2c..66105a90b4c3 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -375,8 +375,8 @@ int __split_huge_page_to_list_to_order(struct page *page, struct list_head *list
int folio_split_unmapped(struct folio *folio, unsigned int new_order);
int min_order_for_split(struct folio *folio);
int split_folio_to_list(struct folio *folio, struct list_head *list);
-bool folio_split_supported(struct folio *folio, unsigned int new_order,
- enum split_type split_type, bool warns);
+int folio_check_splittable(struct folio *folio, unsigned int new_order,
+ enum split_type split_type);
int folio_split(struct folio *folio, unsigned int new_order, struct page *page,
struct list_head *list);
@@ -407,7 +407,7 @@ static inline int split_huge_page_to_order(struct page *page, unsigned int new_o
static inline int try_folio_split_to_order(struct folio *folio,
struct page *page, unsigned int new_order)
{
- if (!folio_split_supported(folio, new_order, SPLIT_TYPE_NON_UNIFORM, /* warns= */ false))
+ if (folio_check_splittable(folio, new_order, SPLIT_TYPE_NON_UNIFORM))
return split_huge_page_to_order(&folio->page, new_order);
return folio_split(folio, new_order, page, NULL);
}
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 041b554c7115..771df0c02a4a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3688,15 +3688,40 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
return 0;
}
-bool folio_split_supported(struct folio *folio, unsigned int new_order,
- enum split_type split_type, bool warns)
+/**
+ * folio_check_splittable() - check if a folio can be split to a given order
+ * @folio: folio to be split
+ * @new_order: the smallest order of the after split folios (since buddy
+ * allocator like split generates folios with orders from @folio's
+ * order - 1 to new_order).
+ * @split_type: uniform or non-uniform split
+ *
+ * folio_check_splittable() checks if @folio can be split to @new_order using
+ * @split_type method. The truncated folio check must come first.
+ *
+ * Context: folio must be locked.
+ *
+ * Return: 0 - @folio can be split to @new_order, otherwise an error number is
+ * returned.
+ */
+int folio_check_splittable(struct folio *folio, unsigned int new_order,
+ enum split_type split_type)
{
+ VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio);
+ /*
+ * Folios that just got truncated cannot get split. Signal to the
+ * caller that there was a race.
+ *
+ * TODO: this will also currently refuse folios without a mapping in the
+ * swapcache (shmem or to-be-anon folios).
+ */
+ if (!folio_test_anon(folio) && !folio->mapping)
+ return -EBUSY;
+
if (folio_test_anon(folio)) {
/* order-1 is not supported for anonymous THP. */
- VM_WARN_ONCE(warns && new_order == 1,
- "Cannot split to order-1 folio");
if (new_order == 1)
- return false;
+ return -EINVAL;
} else if (split_type == SPLIT_TYPE_NON_UNIFORM || new_order) {
if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
!mapping_large_folio_support(folio->mapping)) {
@@ -3717,9 +3742,7 @@ bool folio_split_supported(struct folio *folio, unsigned int new_order,
* case, the mapping does not actually support large
* folios properly.
*/
- VM_WARN_ONCE(warns,
- "Cannot split file folio to non-0 order");
- return false;
+ return -EINVAL;
}
}
@@ -3732,12 +3755,16 @@ bool folio_split_supported(struct folio *folio, unsigned int new_order,
* here.
*/
if ((split_type == SPLIT_TYPE_NON_UNIFORM || new_order) && folio_test_swapcache(folio)) {
- VM_WARN_ONCE(warns,
- "Cannot split swapcache folio to non-0 order");
- return false;
+ return -EINVAL;
}
- return true;
+ if (is_huge_zero_folio(folio))
+ return -EINVAL;
+
+ if (folio_test_writeback(folio))
+ return -EBUSY;
+
+ return 0;
}
static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int new_order,
@@ -3922,7 +3949,6 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
int remap_flags = 0;
int extra_pins, ret;
pgoff_t end = 0;
- bool is_hzp;
VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);
VM_WARN_ON_ONCE_FOLIO(!folio_test_large(folio), folio);
@@ -3930,31 +3956,15 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
if (folio != page_folio(split_at) || folio != page_folio(lock_at))
return -EINVAL;
- /*
- * Folios that just got truncated cannot get split. Signal to the
- * caller that there was a race.
- *
- * TODO: this will also currently refuse shmem folios that are in the
- * swapcache.
- */
- if (!is_anon && !folio->mapping)
- return -EBUSY;
-
if (new_order >= old_order)
return -EINVAL;
- if (!folio_split_supported(folio, new_order, split_type, /* warn = */ true))
- return -EINVAL;
-
- is_hzp = is_huge_zero_folio(folio);
- if (is_hzp) {
- pr_warn_ratelimited("Called split_huge_page for huge zero page\n");
- return -EBUSY;
+ ret = folio_check_splittable(folio, new_order, split_type);
+ if (ret) {
+ VM_WARN_ONCE(ret == -EINVAL, "Tried to split an unsplittable folio");
+ return ret;
}
- if (folio_test_writeback(folio))
- return -EBUSY;
-
if (is_anon) {
/*
* The caller does not necessarily hold an mmap_lock that would
--
2.51.0
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