swap: convert swap_writepage() to use a folio

Removes many calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-41-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_io.c

@@ -180,29 +180,30 @@ int generic_swapfile_activate(struct swap_info_struct *sis,
  */
 int swap_writepage(struct page *page, struct writeback_control *wbc)
 {
+	struct folio *folio = page_folio(page);
 	int ret = 0;
 
-	if (try_to_free_swap(page)) {
-		unlock_page(page);
+	if (folio_free_swap(folio)) {
+		folio_unlock(folio);
 		goto out;
 	}
 	/*
 	 * Arch code may have to preserve more data than just the page
 	 * contents, e.g. memory tags.
 	 */
-	ret = arch_prepare_to_swap(page);
+	ret = arch_prepare_to_swap(&folio->page);
 	if (ret) {
-		set_page_dirty(page);
-		unlock_page(page);
+		folio_mark_dirty(folio);
+		folio_unlock(folio);
 		goto out;
 	}
-	if (frontswap_store(page) == 0) {
-		set_page_writeback(page);
-		unlock_page(page);
-		end_page_writeback(page);
+	if (frontswap_store(&folio->page) == 0) {
+		folio_start_writeback(folio);
+		folio_unlock(folio);
+		folio_end_writeback(folio);
 		goto out;
 	}
-	ret = __swap_writepage(page, wbc);
+	ret = __swap_writepage(&folio->page, wbc);
 out:
 	return ret;
 }