[PATCH v1 12/36] mm: simplify folio_page() and folio_page_idx()

[Wei Yang]

On Thu, Aug 28, 2025 at 12:01:16AM +0200, David Hildenbrand wrote:
>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().
>
>Reviewed-by: Zi Yan <ziy at nvidia.com>
>Signed-off-by: David Hildenbrand <david at redhat.com>

Reviewed-by: Wei Yang <richard.weiyang at gmail.com>

The code looks good, while one nit below.

>---
> 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 2dee79fa2efcf..f6880e3225c5c 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 5ee6ffbdbf831..faf17ca211b4f 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 n)
>+{
>+	return &folio->page + n;
>+}
> 

Curious about why it is in page-flags.h. It seems not related to page-flags.

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

-- 
Wei Yang
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