mm: simplify folio_page() and folio_page_idx()

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

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

Link: https://lkml.kernel.org/r/20250901150359.867252-13-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 2dee79fa2efcf3b3121df440f42c000a88033ef7..f6880e3225c5c92448135414083ae8fe2aae6fd1 100644 (file)
--- 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 5ee6ffbdbf8313f86ebae547a6d60e9ffb65734f..faf17ca211b4fea7a46ecee2c700aca5cd9f4b0e 100644 (file)
--- 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 n)
+{
+       return &folio->page + n;
+}
 
 static __always_inline int PageTail(const struct page *page)
 {