[PATCH v2 1/1] mm: make ref_unless functions unless_zero only

[Gladyshev Ilya]

There are no users of (folio/page)_ref_add_unless(page, nr, u) with
u != 0 [1] and all current users are "internal" for page refcounting API.
This allows us to safely drop this parameter and reduce function
semantics to the "unless zero" cases only.

If needed, these functions for the u!=0 cases can be trivially
reintroduced later using the same atomic_add_unless operations as before.

[1]: The last user was dropped in v5.18 kernel, commit 27674ef6c73f
("mm: remove the extra ZONE_DEVICE struct page refcount"). There is no
trace of discussion as to why this cleanup wasn't done earlier.

Co-developed-by: Gorbunov Ivan <gorbunov.ivan@xxxxxxxxxxxxxx>
Signed-off-by: Gorbunov Ivan <gorbunov.ivan@xxxxxxxxxxxxxx>
Signed-off-by: Gladyshev Ilya <gladyshev.ilya1@xxxxxxxxxxxxxx>
Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
Acked-by: Kiryl Shutsemau <kas@xxxxxxxxxx>
Acked-by: Zi Yan <ziy@xxxxxxxxxx>

---
Changes since v1:
- Rebased on mm-new
- Remove mention of the "next patch" from commit msg

No functional changes

Link to v1: https://lore.kernel.org/all/20260206133328.426921-1-gladyshev.ilya1@xxxxxxxxxxxxxx

---
 include/linux/mm.h       |  2 +-
 include/linux/page_ref.h | 12 ++++++------
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index a68f065399ee..1294d29c8d93 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1506,7 +1506,7 @@ static inline int folio_put_testzero(struct folio *folio)
  */
 static inline bool get_page_unless_zero(struct page *page)
 {
-	return page_ref_add_unless(page, 1, 0);
+	return page_ref_add_unless_zero(page, 1);
 }
 
 static inline struct folio *folio_get_nontail_page(struct page *page)
diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
index 490d0ad6e56d..94d3f0e71c06 100644
--- a/include/linux/page_ref.h
+++ b/include/linux/page_ref.h
@@ -228,18 +228,18 @@ static inline int folio_ref_dec_return(struct folio *folio)
 	return page_ref_dec_return(&folio->page);
 }
 
-static inline bool page_ref_add_unless(struct page *page, int nr, int u)
+static inline bool page_ref_add_unless_zero(struct page *page, int nr)
 {
-	bool ret = atomic_add_unless(&page->_refcount, nr, u);
+	bool ret = atomic_add_unless(&page->_refcount, nr, 0);
 
 	if (page_ref_tracepoint_active(page_ref_mod_unless))
 		__page_ref_mod_unless(page, nr, ret);
 	return ret;
 }
 
-static inline bool folio_ref_add_unless(struct folio *folio, int nr, int u)
+static inline bool folio_ref_add_unless_zero(struct folio *folio, int nr)
 {
-	return page_ref_add_unless(&folio->page, nr, u);
+	return page_ref_add_unless_zero(&folio->page, nr);
 }
 
 /**
@@ -255,12 +255,12 @@ static inline bool folio_ref_add_unless(struct folio *folio, int nr, int u)
  */
 static inline bool folio_try_get(struct folio *folio)
 {
-	return folio_ref_add_unless(folio, 1, 0);
+	return folio_ref_add_unless_zero(folio, 1);
 }
 
 static inline bool folio_ref_try_add(struct folio *folio, int count)
 {
-	return folio_ref_add_unless(folio, count, 0);
+	return folio_ref_add_unless_zero(folio, count);
 }
 
 static inline int page_ref_freeze(struct page *page, int count)
-- 
2.43.0