Message-ID: <20251031162001.670503-4-ziy@nvidia.com>
Date: Fri, 31 Oct 2025 12:20:01 -0400
From: Zi Yan <ziy@...dia.com>
To: linmiaohe@...wei.com,
	david@...hat.com,
	jane.chu@...cle.com
Cc: kernel@...kajraghav.com,
	ziy@...dia.com,
	akpm@...ux-foundation.org,
	mcgrof@...nel.org,
	nao.horiguchi@...il.com,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.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>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Wei Yang <richard.weiyang@...il.com>,
	Yang Shi <shy828301@...il.com>,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [PATCH v5 3/3] mm/huge_memory: fix kernel-doc comments for folio_split() and related.

try_folio_split_to_order(), folio_split, __folio_split(), and
__split_unmapped_folio() do not have correct kernel-doc comment format.
Fix them.

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Reviewed-by: Lance Yang <lance.yang@...ux.dev>
Reviewed-by: Barry Song <baohua@...nel.org>
Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>
Signed-off-by: Zi Yan <ziy@...dia.com>
---
 include/linux/huge_mm.h | 10 +++++----
 mm/huge_memory.c        | 45 ++++++++++++++++++++++-------------------
 2 files changed, 30 insertions(+), 25 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 34f8d8453bf3..cbb2243f8e56 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -386,9 +386,9 @@ static inline int split_huge_page_to_order(struct page *page, unsigned int new_o
 	return split_huge_page_to_list_to_order(page, NULL, new_order);
 }
 
-/*
- * try_folio_split_to_order - try to split a @folio at @page to @new_order using
- * non uniform split.
+/**
+ * try_folio_split_to_order() - try to split a @folio at @page to @new_order
+ * using non uniform split.
  * @folio: folio to be split
  * @page: split to @new_order at the given page
  * @new_order: the target split order
@@ -398,7 +398,7 @@ static inline int split_huge_page_to_order(struct page *page, unsigned int new_o
  * folios are put back to LRU list. Use min_order_for_split() to get the lower
  * bound of @new_order.
  *
- * Return: 0: split is successful, otherwise split failed.
+ * Return: 0 - split is successful, otherwise split failed.
  */
 static inline int try_folio_split_to_order(struct folio *folio,
 		struct page *page, unsigned int new_order)
@@ -486,6 +486,8 @@ static inline spinlock_t *pud_trans_huge_lock(pud_t *pud,
 /**
  * folio_test_pmd_mappable - Can we map this folio with a PMD?
  * @folio: The folio to test
+ *
+ * Return: true - @folio can be mapped, false - @folio cannot be mapped.
  */
 static inline bool folio_test_pmd_mappable(struct folio *folio)
 {
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 0e24bb7e90d0..ad2fc52651a6 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3567,8 +3567,9 @@ static void __split_folio_to_order(struct folio *folio, int old_order,
 		ClearPageCompound(&folio->page);
 }
 
-/*
- * It splits an unmapped @folio to lower order smaller folios in two ways.
+/**
+ * __split_unmapped_folio() - splits an unmapped @folio to lower order folios in
+ * two ways: uniform split or non-uniform split.
  * @folio: the to-be-split folio
  * @new_order: the smallest order of the after split folios (since buddy
  *             allocator like split generates folios with orders from @folio's
@@ -3589,22 +3590,22 @@ static void __split_folio_to_order(struct folio *folio, int old_order,
  *    uniform_split is false.
  *
  * The high level flow for these two methods are:
- * 1. uniform split: a single __split_folio_to_order() is called to split the
- *    @folio into @new_order, then we traverse all the resulting folios one by
- *    one in PFN ascending order and perform stats, unfreeze, adding to list,
- *    and file mapping index operations.
- * 2. non-uniform split: in general, folio_order - @new_order calls to
- *    __split_folio_to_order() are made in a for loop to split the @folio
- *    to one lower order at a time. The resulting small folios are processed
- *    like what is done during the traversal in 1, except the one containing
- *    @page, which is split in next for loop.
+ * 1. uniform split: @xas is split with no expectation of failure and a single
+ *    __split_folio_to_order() is called to split the @folio into @new_order
+ *    along with stats update.
+ * 2. non-uniform split: folio_order - @new_order calls to
+ *    __split_folio_to_order() are expected to be made in a for loop to split
+ *    the @folio to one lower order at a time. The folio containing @page is
+ *    split in each iteration. @xas is split into half in each iteration and
+ *    can fail. A failed @xas split leaves split folios as is without merging
+ *    them back.
  *
  * After splitting, the caller's folio reference will be transferred to the
  * folio containing @page. The caller needs to unlock and/or free after-split
  * folios if necessary.
  *
- * For !uniform_split, when -ENOMEM is returned, the original folio might be
- * split. The caller needs to check the input folio.
+ * Return: 0 - successful, <0 - failed (if -ENOMEM is returned, @folio might be
+ * split but not to @new_order, the caller needs to check)
  */
 static int __split_unmapped_folio(struct folio *folio, int new_order,
 		struct page *split_at, struct xa_state *xas,
@@ -3722,8 +3723,8 @@ bool uniform_split_supported(struct folio *folio, unsigned int new_order,
 	return true;
 }
 
-/*
- * __folio_split: split a folio at @split_at to a @new_order folio
+/**
+ * __folio_split() - split a folio at @split_at to a @new_order folio
  * @folio: folio to split
  * @new_order: the order of the new folio
  * @split_at: a page within the new folio
@@ -3741,7 +3742,7 @@ bool uniform_split_supported(struct folio *folio, unsigned int new_order,
  * 1. for uniform split, @lock_at points to one of @folio's subpages;
  * 2. for buddy allocator like (non-uniform) split, @lock_at points to @folio.
  *
- * return: 0: successful, <0 failed (if -ENOMEM is returned, @folio might be
+ * Return: 0 - successful, <0 - failed (if -ENOMEM is returned, @folio might be
  * split but not to @new_order, the caller needs to check)
  */
 static int __folio_split(struct folio *folio, unsigned int new_order,
@@ -4130,14 +4131,13 @@ int __split_huge_page_to_list_to_order(struct page *page, struct list_head *list
 				unmapped);
 }
 
-/*
- * folio_split: split a folio at @split_at to a @new_order folio
+/**
+ * folio_split() - split a folio at @split_at to a @new_order folio
  * @folio: folio to split
  * @new_order: the order of the new folio
  * @split_at: a page within the new folio
- *
- * return: 0: successful, <0 failed (if -ENOMEM is returned, @folio might be
- * split but not to @new_order, the caller needs to check)
+ * @list: after-split folios are added to @list if not null, otherwise to LRU
+ *        list
  *
  * It has the same prerequisites and returns as
  * split_huge_page_to_list_to_order().
@@ -4151,6 +4151,9 @@ int __split_huge_page_to_list_to_order(struct page *page, struct list_head *list
  * [order-4, {order-3}, order-3, order-5, order-6, order-7, order-8].
  *
  * After split, folio is left locked for caller.
+ *
+ * Return: 0 - successful, <0 - failed (if -ENOMEM is returned, @folio might be
+ * split but not to @new_order, the caller needs to check)
  */
 int folio_split(struct folio *folio, unsigned int new_order,
 		struct page *split_at, struct list_head *list)
-- 
2.51.0

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