[PATCH v3 5/6] mm: move folio_index to mm/swap.h and remove no longer needed helper

[Kairui Song <ryncsn@gmail.com>]

From: Kairui Song <kasong@tencent.com>

There are no remaining users of folio_index() outside the mm subsystem.
Move it to mm/swap.h to co-locate it with swap_cache_index(), eliminating
a forward declaration, and a function call overhead.

Also remove the helper that was used to fix circular header dependency
issue.

Signed-off-by: Kairui Song <kasong@tencent.com>
---
 include/linux/pagemap.h | 20 --------------------
 mm/gup.c                |  1 +
 mm/memfd.c              |  1 +
 mm/migrate.c            |  1 +
 mm/page-writeback.c     |  1 +
 mm/swap.h               | 18 ++++++++++++++++++
 mm/swapfile.c           |  6 ------
 7 files changed, 22 insertions(+), 26 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 0c9aff5ec77f..627cb0338e5d 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -884,26 +884,6 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
 			mapping_gfp_mask(mapping));
 }
 
-extern pgoff_t __folio_swap_cache_index(struct folio *folio);
-
-/**
- * folio_index - File index of a folio.
- * @folio: The folio.
- *
- * For a folio which is either in the page cache or the swap cache,
- * return its index within the address_space it belongs to.  If you know
- * the page is definitely in the page cache, you can look at the folio's
- * index directly.
- *
- * Return: The index (offset in units of pages) of a folio in its file.
- */
-static inline pgoff_t folio_index(struct folio *folio)
-{
-	if (unlikely(folio_test_swapcache(folio)))
-		return __folio_swap_cache_index(folio);
-	return folio->index;
-}
-
 /**
  * folio_next_index - Get the index of the next folio.
  * @folio: The current folio.
diff --git a/mm/gup.c b/mm/gup.c
index f32168339390..91bbf57579f0 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -26,6 +26,7 @@
 #include <asm/tlbflush.h>
 
 #include "internal.h"
+#include "swap.h"
 
 struct follow_page_context {
 	struct dev_pagemap *pgmap;
diff --git a/mm/memfd.c b/mm/memfd.c
index c64df1343059..ab367e61553d 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -20,6 +20,7 @@
 #include <linux/memfd.h>
 #include <linux/pid_namespace.h>
 #include <uapi/linux/memfd.h>
+#include "swap.h"
 
 /*
  * We need a tag: a new tag would expand every xa_node by 8 bytes,
diff --git a/mm/migrate.c b/mm/migrate.c
index f3ee6d8d5e2e..662e5dc44b33 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -50,6 +50,7 @@
 #include <trace/events/migrate.h>
 
 #include "internal.h"
+#include "swap.h"
 
 bool isolate_movable_page(struct page *page, isolate_mode_t mode)
 {
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 20e1d76f1eba..9ff44b64d3d6 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -41,6 +41,7 @@
 #include <trace/events/writeback.h>
 
 #include "internal.h"
+#include "swap.h"
 
 /*
  * Sleep at most 200ms at a time in balance_dirty_pages().
diff --git a/mm/swap.h b/mm/swap.h
index 6f4a3f927edb..521bf510ec75 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -201,4 +201,22 @@ static inline int swap_zeromap_batch(swp_entry_t entry, int max_nr,
 
 #endif /* CONFIG_SWAP */
 
+/**
+ * folio_index - File index of a folio.
+ * @folio: The folio.
+ *
+ * For a folio which is either in the page cache or the swap cache,
+ * return its index within the address_space it belongs to.  If you know
+ * the folio is definitely in the page cache, you can look at the folio's
+ * index directly.
+ *
+ * Return: The index (offset in units of pages) of a folio in its file.
+ */
+static inline pgoff_t folio_index(struct folio *folio)
+{
+	if (unlikely(folio_test_swapcache(folio)))
+		return swap_cache_index(folio->swap);
+	return folio->index;
+}
+
 #endif /* _MM_SWAP_H */
diff --git a/mm/swapfile.c b/mm/swapfile.c
index b86637cfb17a..9fe58284079d 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3671,12 +3671,6 @@ struct address_space *swapcache_mapping(struct folio *folio)
 }
 EXPORT_SYMBOL_GPL(swapcache_mapping);
 
-pgoff_t __folio_swap_cache_index(struct folio *folio)
-{
-	return swap_cache_index(folio->swap);
-}
-EXPORT_SYMBOL_GPL(__folio_swap_cache_index);
-
 /*
  * add_swap_count_continuation - called when a swap count is duplicated
  * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
-- 
2.49.0