mm: move folio_index to mm/swap.h and remove no longer needed helper

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.

Link: https://lkml.kernel.org/r/20250430181052.55698-6-ryncsn@gmail.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Chao Yu <chao@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Chris Mason <clm@fb.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Sterba <dsterba@suse.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Joanne Koong <joannelkoong@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Qu Wenruo <wqu@suse.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 0 insertions, 20 deletions

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index b2c2ff8de046..5d66786867eb 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.