[PATCH 0/2] fs/dax: Clean up busy page lookup helpers

[PATCH 0/2] fs/dax: Clean up busy page lookup helpers

[Kaitao Cheng]

The dax_layout_busy_page() and dax_layout_busy_page_range() helpers were
originally exposed so filesystems could find pinned DAX pages before
changing file layouts. Filesystem callers now use dax_break_layout(),
which provides the complete operation, leaving no direct users of these
lookup helpers outside fs/dax.c.

Remove the unused whole-mapping wrapper and make the remaining range
helper private to fs/dax.c. This reduces the exported DAX interface with
no functional change.

Kaitao Cheng (2):
  fs/dax: Remove unused dax_layout_busy_page()
  fs/dax: Make dax_layout_busy_page_range() static

 fs/dax.c            | 24 ++++++++----------------
 include/linux/dax.h | 12 ------------
 2 files changed, 8 insertions(+), 28 deletions(-)

-- 
2.50.1 (Apple Git-155)

[PATCH 1/2] fs/dax: Remove unused dax_layout_busy_page()

[Kaitao Cheng]

From: Kaitao Cheng <chengkaitao@kylinos.cn>

dax_layout_busy_page() used to let filesystems scan an entire DAX
mapping for pinned pages. All callers now use dax_break_layout(),
which also handles waiting for busy pages and deleting DAX mapping
entries once the range becomes idle.

The remaining function is only a wrapper around
dax_layout_busy_page_range() and has no in-tree users. Remove it
together with its declaration, !CONFIG_FS_DAX stub, and exported
symbol.

Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
---
 fs/dax.c            | 6 ------
 include/linux/dax.h | 6 ------
 2 files changed, 12 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index dad4efea7964..1e19e4a354ce 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -841,12 +841,6 @@ struct page *dax_layout_busy_page_range(struct address_space *mapping,
 }
 EXPORT_SYMBOL_GPL(dax_layout_busy_page_range);
 
-struct page *dax_layout_busy_page(struct address_space *mapping)
-{
-	return dax_layout_busy_page_range(mapping, 0, LLONG_MAX);
-}
-EXPORT_SYMBOL_GPL(dax_layout_busy_page);
-
 static int __dax_invalidate_entry(struct address_space *mapping,
 				  pgoff_t index, bool trunc)
 {
diff --git a/include/linux/dax.h b/include/linux/dax.h
index fe6c3ded1b50..05e59e45a1c2 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -155,7 +155,6 @@ int dax_writeback_mapping_range(struct address_space *mapping,
 		struct dax_device *dax_dev, struct writeback_control *wbc);
 int dax_folio_reset_order(struct folio *folio);
 
-struct page *dax_layout_busy_page(struct address_space *mapping);
 struct page *dax_layout_busy_page_range(struct address_space *mapping, loff_t start, loff_t end);
 dax_entry_t dax_lock_folio(struct folio *folio);
 void dax_unlock_folio(struct folio *folio, dax_entry_t cookie);
@@ -173,11 +172,6 @@ static inline int fs_dax_get(struct dax_device *dax_dev, void *holder,
 {
 	return -EOPNOTSUPP;
 }
-static inline struct page *dax_layout_busy_page(struct address_space *mapping)
-{
-	return NULL;
-}
-
 static inline struct page *dax_layout_busy_page_range(struct address_space *mapping, pgoff_t start, pgoff_t nr_pages)
 {
 	return NULL;
-- 
2.50.1 (Apple Git-155)

Re: [PATCH 1/2] fs/dax: Remove unused dax_layout_busy_page()

[Muchun Song]

> On Sep 4, 2026, at 23:27, Kaitao Cheng <kaitao.cheng@linux.dev> wrote:
> 
> From: Kaitao Cheng <chengkaitao@kylinos.cn>
> 
> dax_layout_busy_page() used to let filesystems scan an entire DAX
> mapping for pinned pages. All callers now use dax_break_layout(),
> which also handles waiting for busy pages and deleting DAX mapping
> entries once the range becomes idle.
> 
> The remaining function is only a wrapper around
> dax_layout_busy_page_range() and has no in-tree users. Remove it
> together with its declaration, !CONFIG_FS_DAX stub, and exported
> symbol.
> 
> Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>

Acked-by: Muchun Song <muchun.song@linux.dev>

Thanks.

[PATCH 2/2] fs/dax: Make dax_layout_busy_page_range() static

[Kaitao Cheng]

From: Kaitao Cheng <chengkaitao@kylinos.cn>

dax_layout_busy_page_range() no longer has callers outside fs/dax.c.
Keeping the range helper exported unnecessarily exposes a low-level
implementation detail.

Make the helper static and remove its export and header definitions.

Also fix the stale dax_layout_busy_page_range() comment to match the
implementation.

Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
---
 fs/dax.c            | 18 ++++++++----------
 include/linux/dax.h |  6 ------
 2 files changed, 8 insertions(+), 16 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 1e19e4a354ce..c6ad9533aa54 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -770,24 +770,23 @@ static void *grab_mapping_entry(struct xa_state *xas,
 
 /**
  * dax_layout_busy_page_range - find first pinned page in @mapping
- * @mapping: address space to scan for a page with ref count > 1
+ * @mapping: address space to scan for a pinned page
  * @start: Starting offset. Page containing 'start' is included.
  * @end: End offset. Page containing 'end' is included. If 'end' is LLONG_MAX,
  *       pages from 'start' till the end of file are included.
  *
- * DAX requires ZONE_DEVICE mapped pages. These pages are never
- * 'onlined' to the page allocator so they are considered idle when
- * page->count == 1. A filesystem uses this interface to determine if
- * any page in the mapping is busy, i.e. for DMA, or other
- * get_user_pages() usages.
+ * DAX requires ZONE_DEVICE mapped pages. A page is considered busy when
+ * folio_ref_count(folio) exceeds folio_mapcount(folio). This helper is
+ * used to determine if any page in the mapping is busy, i.e. for DMA,
+ * or other get_user_pages() usages.
  *
  * It is expected that the filesystem is holding locks to block the
  * establishment of new mappings in this address_space. I.e. it expects
- * to be able to run unmap_mapping_range() and subsequently not race
+ * to be able to run unmap_mapping_pages() and subsequently not race
  * mapping_mapped() becoming true.
  */
-struct page *dax_layout_busy_page_range(struct address_space *mapping,
-					loff_t start, loff_t end)
+static struct page *dax_layout_busy_page_range(struct address_space *mapping,
+					       loff_t start, loff_t end)
 {
 	void *entry;
 	unsigned int scanned = 0;
@@ -839,7 +838,6 @@ struct page *dax_layout_busy_page_range(struct address_space *mapping,
 	xas_unlock_irq(&xas);
 	return page;
 }
-EXPORT_SYMBOL_GPL(dax_layout_busy_page_range);
 
 static int __dax_invalidate_entry(struct address_space *mapping,
 				  pgoff_t index, bool trunc)
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 05e59e45a1c2..f2d47975d905 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -155,7 +155,6 @@ int dax_writeback_mapping_range(struct address_space *mapping,
 		struct dax_device *dax_dev, struct writeback_control *wbc);
 int dax_folio_reset_order(struct folio *folio);
 
-struct page *dax_layout_busy_page_range(struct address_space *mapping, loff_t start, loff_t end);
 dax_entry_t dax_lock_folio(struct folio *folio);
 void dax_unlock_folio(struct folio *folio, dax_entry_t cookie);
 dax_entry_t dax_lock_mapping_entry(struct address_space *mapping,
@@ -172,11 +171,6 @@ static inline int fs_dax_get(struct dax_device *dax_dev, void *holder,
 {
 	return -EOPNOTSUPP;
 }
-static inline struct page *dax_layout_busy_page_range(struct address_space *mapping, pgoff_t start, pgoff_t nr_pages)
-{
-	return NULL;
-}
-
 static inline int dax_writeback_mapping_range(struct address_space *mapping,
 		struct dax_device *dax_dev, struct writeback_control *wbc)
 {
-- 
2.50.1 (Apple Git-155)

Re: [PATCH 2/2] fs/dax: Make dax_layout_busy_page_range() static

[Muchun Song]

> On Sep 4, 2026, at 23:27, Kaitao Cheng <kaitao.cheng@linux.dev> wrote:
> 
> From: Kaitao Cheng <chengkaitao@kylinos.cn>
> 
> dax_layout_busy_page_range() no longer has callers outside fs/dax.c.
> Keeping the range helper exported unnecessarily exposes a low-level
> implementation detail.
> 
> Make the helper static and remove its export and header definitions.
> 
> Also fix the stale dax_layout_busy_page_range() comment to match the
> implementation.
> 
> Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>

Acked-by: Muchun Song <muchun.song@linux.dev>

Thanks.