mm: pass a folio to __swap_writepage()

Both callers now have a folio, so pass that in instead of the page. 
Removes a few hidden calls to compound_head().

Link: https://lkml.kernel.org/r/20231213215842.671461-3-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_io.c

@@ -201,7 +201,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
 		folio_end_writeback(folio);
 		return 0;
 	}
-	__swap_writepage(&folio->page, wbc);
+	__swap_writepage(folio, wbc);
 	return 0;
 }
 
@@ -368,22 +368,22 @@ static void swap_writepage_bdev_async(struct page *page,
 	submit_bio(bio);
 }
 
-void __swap_writepage(struct page *page, struct writeback_control *wbc)
+void __swap_writepage(struct folio *folio, struct writeback_control *wbc)
 {
-	struct swap_info_struct *sis = page_swap_info(page);
+	struct swap_info_struct *sis = swp_swap_info(folio->swap);
 
-	VM_BUG_ON_PAGE(!PageSwapCache(page), page);
+	VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio);
 	/*
 	 * ->flags can be updated non-atomicially (scan_swap_map_slots),
 	 * but that will never affect SWP_FS_OPS, so the data_race
 	 * is safe.
 	 */
 	if (data_race(sis->flags & SWP_FS_OPS))
-		swap_writepage_fs(page, wbc);
+		swap_writepage_fs(&folio->page, wbc);
 	else if (sis->flags & SWP_SYNCHRONOUS_IO)
-		swap_writepage_bdev_sync(page, wbc, sis);
+		swap_writepage_bdev_sync(&folio->page, wbc, sis);
 	else
-		swap_writepage_bdev_async(page, wbc, sis);
+		swap_writepage_bdev_async(&folio->page, wbc, sis);
 }
 
 void swap_write_unplug(struct swap_iocb *sio)

mm/swap.h

@@ -19,7 +19,7 @@ static inline void swap_read_unplug(struct swap_iocb *plug)
 }
 void swap_write_unplug(struct swap_iocb *sio);
 int swap_writepage(struct page *page, struct writeback_control *wbc);
-void __swap_writepage(struct page *page, struct writeback_control *wbc);
+void __swap_writepage(struct folio *folio, struct writeback_control *wbc);
 
 /* linux/mm/swap_state.c */
 /* One swap address space for each 64M swap space */

mm/zswap.c

@@ -1446,7 +1446,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
 	folio_set_reclaim(folio);
 
 	/* start writeback */
-	__swap_writepage(&folio->page, &wbc);
+	__swap_writepage(folio, &wbc);
 	folio_put(folio);
 
 	return 0;