linux-kernel - [PATCH v1] mm: convert folio

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Message-ID: <20250923140058.2020023-1-david@redhat.com>
Date: Tue, 23 Sep 2025 16:00:58 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
	David Hildenbrand <david@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>
Subject: [PATCH v1] mm: convert folio_page() back to a macro

In commit 73b3294b1152 ("mm: simplify folio_page() and folio_page_idx()")
we converted folio_page() into a static inline function. However
briefly afterwards in commit a847b17009ec ("mm: constify highmem related
functions for improved const-correctness") we had to add some nasty
const-away casting to make the compiler happy when checking const
correctness.

So let's just convert it back to a simple macro so the compiler can
check const correctness properly. There is the alternative of
using a _Generic() similar to page_folio(), but there is not a lot of
benefit compared to just using a simple macro.

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Mike Rapoport <rppt@...nel.org>
Cc: Suren Baghdasaryan <surenb@...gle.com>
Cc: Michal Hocko <mhocko@...e.com>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 include/linux/page-flags.h | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 568011930e358..48e27768e7ba9 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -316,10 +316,7 @@ 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.
  */
-static inline struct page *folio_page(const struct folio *folio, unsigned long n)
-{
-	return (struct page *)(&folio->page + n);
-}
+#define folio_page(folio, n)	(&(folio)->page + (n))
 
 static __always_inline int PageTail(const struct page *page)
 {
-- 
2.51.0