[PATCH v6 08/15] linux/mm.h: move folio_next() to mm/folio_next.h

[Max Kellermann]

Prepare to reduce dependencies on linux/mm.h.

folio_next() is used by linux/bio.h.  Moving it to a separate lean
header will allow us to avoid the dependency on linux/mm.h.

Having a one-function header may seem excessive, but there is hardly
another way if we want to distangle linux/mm.h from linux/bio.h.  If
one day, say, folio_prev() gets added, we can still rename the header
to something like folio_iterator.h, but until that happens, this
folio_next.h header seems like the best trade-off to reduce
dependencies.

Signed-off-by: Max Kellermann <max.kellermann@xxxxxxxxx>
---
 include/linux/mm.h            | 20 +-------------------
 include/linux/mm/folio_next.h | 27 +++++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 19 deletions(-)
 create mode 100644 include/linux/mm/folio_next.h

diff --git a/include/linux/mm.h b/include/linux/mm.h
index b11bbbdd2754..7be75960e7e1 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2,6 +2,7 @@
 #ifndef _LINUX_MM_H
 #define _LINUX_MM_H
 
+#include <linux/mm/folio_next.h>
 #include <linux/mm/folio_size.h>
 #include <linux/mm/page_address.h>
 #include <linux/mm/page_section.h>
@@ -1916,25 +1917,6 @@ static inline void set_page_links(struct page *page, enum zone_type zone,
 #define MAX_FOLIO_NR_PAGES	MAX_ORDER_NR_PAGES
 #endif
 
-/**
- * folio_next - Move to the next physical folio.
- * @folio: The folio we're currently operating on.
- *
- * If you have physically contiguous memory which may span more than
- * one folio (eg a &struct bio_vec), use this function to move from one
- * folio to the next.  Do not use it if the memory is only virtually
- * contiguous as the folios are almost certainly not adjacent to each
- * other.  This is the folio equivalent to writing ``page++``.
- *
- * Context: We assume that the folios are refcounted and/or locked at a
- * higher level and do not adjust the reference counts.
- * Return: The next struct folio.
- */
-static inline struct folio *folio_next(struct folio *folio)
-{
-	return (struct folio *)folio_page(folio, folio_nr_pages(folio));
-}
-
 /**
  * folio_likely_mapped_shared - Estimate if the folio is mapped into the page
  *				tables of more than one MM
diff --git a/include/linux/mm/folio_next.h b/include/linux/mm/folio_next.h
new file mode 100644
index 000000000000..7016e303439c
--- /dev/null
+++ b/include/linux/mm/folio_next.h
@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_MM_FOLIO_NEXT_H
+#define _LINUX_MM_FOLIO_NEXT_H
+
+#include <linux/mm/folio_size.h> // for folio_nr_pages()
+#include <linux/mm/page_address.h> // for nth_page(), needed by folio_page()
+
+/**
+ * folio_next - Move to the next physical folio.
+ * @folio: The folio we're currently operating on.
+ *
+ * If you have physically contiguous memory which may span more than
+ * one folio (eg a &struct bio_vec), use this function to move from one
+ * folio to the next.  Do not use it if the memory is only virtually
+ * contiguous as the folios are almost certainly not adjacent to each
+ * other.  This is the folio equivalent to writing ``page++``.
+ *
+ * Context: We assume that the folios are refcounted and/or locked at a
+ * higher level and do not adjust the reference counts.
+ * Return: The next struct folio.
+ */
+static inline struct folio *folio_next(struct folio *folio)
+{
+	return (struct folio *)folio_page(folio, folio_nr_pages(folio));
+}
+
+#endif /* _LINUX_MM_FOLIO_NEXT_H */
-- 
2.39.2