mm: make folio page count functions return unsigned

As raised by Andrew [1], a folio/compound page never spans a negative
number of pages.  Consequently, let's use "unsigned long" instead of
"long" consistently for folio_nr_pages(), folio_large_nr_pages() and
compound_nr().

Using "unsigned long" as return value is fine, because even
"(long)-folio_nr_pages()" will keep on working as expected.  Using
"unsigned int" instead would actually break these use cases.

This patch takes the first step changing these to return unsigned long
(and making drm_gem_get_pages() use the new types instead of replacing
min()).

In the future, we might want to make more callers of these functions to
consistently use "unsigned long".


Link: https://lore.kernel.org/linux-mm/20250503182858.5a02729fcffd6d4723afcfc2@linux-foundation.org/
Link: https://lkml.kernel.org/r/20250826153721.GA23292@cathedrallabs.org
Link: https://lore.kernel.org/linux-mm/20250503182858.5a02729fcffd6d4723afcfc2@linux-foundation.org/ [1]
Signed-off-by: Aristeu Rozanski <aris@ruivo.org>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

2 files changed, 6 insertions, 6 deletions

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 6a44351e58b7..5dbcf91ff73c 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -621,7 +621,7 @@ struct page **drm_gem_get_pages(struct drm_gem_object *obj)
 	struct page **pages;
 	struct folio *folio;
 	struct folio_batch fbatch;
-	long i, j, npages;
+	unsigned long i, j, npages;
 
 	if (WARN_ON(!obj->filp))
 		return ERR_PTR(-EINVAL);
@@ -645,7 +645,7 @@ struct page **drm_gem_get_pages(struct drm_gem_object *obj)
 
 	i = 0;
 	while (i < npages) {
-		long nr;
+		unsigned long nr;
 		folio = shmem_read_folio_gfp(mapping, i,
 				mapping_gfp_mask(mapping));
 		if (IS_ERR(folio))
diff --git a/include/linux/mm.h b/include/linux/mm.h
index da6e0abad2cb..8f5b4df9b166 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1018,12 +1018,12 @@ static inline unsigned int folio_large_order(const struct folio *folio)
 }
 
 #ifdef NR_PAGES_IN_LARGE_FOLIO
-static inline long folio_large_nr_pages(const struct folio *folio)
+static inline unsigned long folio_large_nr_pages(const struct folio *folio)
 {
 	return folio->_nr_pages;
 }
 #else
-static inline long folio_large_nr_pages(const struct folio *folio)
+static inline unsigned long folio_large_nr_pages(const struct folio *folio)
 {
 	return 1L << folio_large_order(folio);
 }
@@ -2062,7 +2062,7 @@ static inline void set_page_links(struct page *page, enum zone_type zone,
  *
  * Return: A positive power of two.
  */
-static inline long folio_nr_pages(const struct folio *folio)
+static inline unsigned long folio_nr_pages(const struct folio *folio)
 {
 	if (!folio_test_large(folio))
 		return 1;
@@ -2097,7 +2097,7 @@ static inline long folio_nr_pages(const struct folio *folio)
  * page.  compound_nr() can be called on a tail page, and is defined to
  * return 1 in that case.
  */
-static inline long compound_nr(const struct page *page)
+static inline unsigned long compound_nr(const struct page *page)
 {
 	const struct folio *folio = (struct folio *)page;