[PATCH RFC 13/35] mm: simplify folio_page() and folio_page_idx()

David Hildenbrand
2025-08-21T21:33:38Z

Now that a single folio/compound page can no longer span memory sections
in problematic kernel configurations, we can stop using nth_page().

While at it, turn both macros into static inline functions and add
kernel doc for folio_page_idx().

Signed-off-by: David Hildenbrand <david@redhat.com>
---
include/linux/mm.h | 16 ++++++++++++++--
include/linux/page-flags.h | 5 ++++-
2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 48a985e17ef4e..ef360b72cb05c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -210,10 +210,8 @@ extern unsigned long sysctl_admin_reserve_kbytes;

#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
#define nth_page(page,n) pfn_to_page(page_to_pfn((page)) + (n))
-#define folio_page_idx(folio, p) (page_to_pfn(p) - folio_pfn(folio))
#else
#define nth_page(page,n) ((page) + (n))
-#define folio_page_idx(folio, p) ((p) - &(folio)->page)
#endif

/* to align the pointer to the (next) page boundary */
@@ -225,6 +223,20 @@ extern unsigned long sysctl_admin_reserve_kbytes;
/* test whether an address (unsigned long or pointer) is aligned to PAGE_SIZE */
#define PAGE_ALIGNED(addr) IS_ALIGNED((unsigned long)(addr), PAGE_SIZE)

+/**
+ * folio_page_idx - Return the number of a page in a folio.
+ * @folio: The folio.
+ * @page: The folio page.
+ *
+ * This function expects that the page is actually part of the folio.
+ * The returned number is relative to the start of the folio.
+ */
+static inline unsigned long folio_page_idx(const struct folio *folio,
+ const struct page *page)
+{
+ return page - &folio->page;
+}
+
static inline struct folio *lru_to_folio(struct list_head *head)
{
return list_entry((head)->prev, struct folio, lru);
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index d53a86e68c89b..080ad10c0defc 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -316,7 +316,10 @@ static __always_inline unsigned long _compound_head(const struct page *page)
* check that the page number lies within @folio; the caller is presumed
* to have a reference to the page.
*/
-#define folio_page(folio, n) nth_page(&(folio)->page, n)
+static inline struct page *folio_page(struct folio *folio, unsigned long nr)
+{
+ return &folio->page + nr;
+}

static __always_inline int PageTail(const struct page *page)
{
--
2.50.1