mm: drop page_index and simplify folio_index

There are two helpers for retrieving the index within address space for
mixed usage of swap cache and page cache:

- page_index
- folio_index

This commit drops page_index, as we have eliminated all users, and
converts folio_index's helper __page_file_index to use folio to avoid the
page conversion.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Kairui Song <[email protected]>
Reviewed-by: "Huang, Ying" <[email protected]>
Cc: Anna Schumaker <[email protected]>
Cc: Barry Song <[email protected]>
Cc: Chao Yu <[email protected]>
Cc: Chris Li <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: David Howells <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Ilya Dryomov <[email protected]>
Cc: Jaegeuk Kim <[email protected]>
Cc: Jeff Layton <[email protected]>
Cc: Marc Dionne <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: NeilBrown <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Ryusuke Konishi <[email protected]>
Cc: Trond Myklebust <[email protected]>
Cc: Xiubo Li <[email protected]>
Cc: Yosry Ahmed <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

include/linux/mm.h

@@ -2295,19 +2295,6 @@ static inline void *folio_address(const struct folio *folio)
 	return page_address(&folio->page);
 }
 
-extern pgoff_t __page_file_index(struct page *page);
-
-/*
- * Return the pagecache index of the passed page.  Regular pagecache pages
- * use ->index whereas swapcache pages use swp_offset(->private)
- */
-static inline pgoff_t page_index(struct page *page)
-{
-	if (unlikely(PageSwapCache(page)))
-		return __page_file_index(page);
-	return page->index;
-}
-
 /*
  * Return true only if the page has been allocated with
  * ALLOC_NO_WATERMARKS and the low watermark was not

include/linux/pagemap.h

@@ -792,7 +792,7 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
 			mapping_gfp_mask(mapping));
 }
 
-#define swapcache_index(folio)	__page_file_index(&(folio)->page)
+extern pgoff_t __folio_swap_cache_index(struct folio *folio);
 
 /**
  * folio_index - File index of a folio.
@@ -807,9 +807,9 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
  */
 static inline pgoff_t folio_index(struct folio *folio)
 {
-        if (unlikely(folio_test_swapcache(folio)))
-                return swapcache_index(folio);
-        return folio->index;
+	if (unlikely(folio_test_swapcache(folio)))
+		return __folio_swap_cache_index(folio);
+	return folio->index;
 }
 
 /**

mm/swapfile.c

@@ -3449,12 +3449,11 @@ struct address_space *swapcache_mapping(struct folio *folio)
 }
 EXPORT_SYMBOL_GPL(swapcache_mapping);
 
-pgoff_t __page_file_index(struct page *page)
+pgoff_t __folio_swap_cache_index(struct folio *folio)
 {
-	swp_entry_t swap = page_swap_entry(page);
-	return swp_offset(swap);
+	return swp_offset(folio->swap);
 }
-EXPORT_SYMBOL_GPL(__page_file_index);
+EXPORT_SYMBOL_GPL(__folio_swap_cache_index);
 
 /*
  * add_swap_count_continuation - called when a swap count is duplicated