mm: remove page_file_offset and folio_file_pos

These two helpers were useful for mixed usage of swap cache and page
cache, which help retrieve the corresponding file or swap device offset of
a page or folio.

They were introduced in commit f981c595 ("mm: methods for teaching
filesystems about PG_swapcache pages") and used in commit d56b4ddf
("nfs: teach the NFS client how to treat PG_swapcache pages"), suppose to
be used with direct_IO for swap over fs.

But after commit e1209d3a ("mm: introduce ->swap_rw and use it for
reads from SWP_FS_OPS swap-space"), swap with direct_IO is no more, and
swap cache mapping is never exposed to fs.

Now we have dropped all users of page_file_offset and folio_file_pos, so
they can be deleted.

Link: https://lkml.kernel.org/r/20240521175854.96038-10-ryncsn@gmail.comSigned-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Anna Schumaker <anna@kernel.org>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Chao Yu <chao@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ilya Dryomov <idryomov@gmail.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Marc Dionne <marc.dionne@auristor.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: NeilBrown <neilb@suse.de>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Xiubo Li <xiubli@redhat.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/pagemap.h

@@ -932,11 +932,6 @@ static inline loff_t page_offset(struct page *page)
 	return ((loff_t)page->index) << PAGE_SHIFT;
 }
 
-static inline loff_t page_file_offset(struct page *page)
-{
-	return ((loff_t)page_index(page)) << PAGE_SHIFT;
-}
-
 /**
  * folio_pos - Returns the byte position of this folio in its file.
  * @folio: The folio.
@@ -946,18 +941,6 @@ static inline loff_t folio_pos(struct folio *folio)
 	return page_offset(&folio->page);
 }
 
-/**
- * folio_file_pos - Returns the byte position of this folio in its file.
- * @folio: The folio.
- *
- * This differs from folio_pos() for folios which belong to a swap file.
- * NFS is the only filesystem today which needs to use folio_file_pos().
- */
-static inline loff_t folio_file_pos(struct folio *folio)
-{
-	return page_file_offset(&folio->page);
-}
-
 /*
  * Get the offset in PAGE_SIZE (even for hugetlb folios).
  */