xfs: refactor the tail of xfs_writepage_map

Rejuggle how we deal with the different error vs non-error and have
ioends vs not have ioend cases to keep the fast path streamlined, and
the duplicate code at a minimum.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_aops.c

@@ -854,7 +854,14 @@ xfs_writepage_map(
 	 * submission of outstanding ioends on the writepage context so they are
 	 * treated correctly on error.
 	 */
-	if (count) {
+	if (unlikely(error)) {
+		if (!count) {
+			xfs_aops_discard_page(page);
+			ClearPageUptodate(page);
+			unlock_page(page);
+			goto done;
+		}
+
 		/*
 		 * If the page was not fully cleaned, we need to ensure that the
 		 * higher layers come back to it correctly.  That means we need
@@ -863,43 +870,35 @@ xfs_writepage_map(
 		 * so another attempt to write this page in this writeback sweep
 		 * will be made.
 		 */
-		if (error) {
-			set_page_writeback_keepwrite(page);
-		} else {
-			clear_page_dirty_for_io(page);
-			set_page_writeback(page);
-		}
-		unlock_page(page);
-
-		/*
-		 * Preserve the original error if there was one, otherwise catch
-		 * submission errors here and propagate into subsequent ioend
-		 * submissions.
-		 */
-		list_for_each_entry_safe(ioend, next, &submit_list, io_list) {
-			int error2;
-
-			list_del_init(&ioend->io_list);
-			error2 = xfs_submit_ioend(wbc, ioend, error);
-			if (error2 && !error)
-				error = error2;
-		}
-	} else if (error) {
-		xfs_aops_discard_page(page);
-		ClearPageUptodate(page);
-		unlock_page(page);
+		set_page_writeback_keepwrite(page);
 	} else {
-		/*
-		 * We can end up here with no error and nothing to write if we
-		 * race with a partial page truncate on a sub-page block sized
-		 * filesystem. In that case we need to mark the page clean.
-		 */
 		clear_page_dirty_for_io(page);
 		set_page_writeback(page);
-		unlock_page(page);
-		end_page_writeback(page);
 	}
 
+	unlock_page(page);
+
+	/*
+	 * Preserve the original error if there was one, otherwise catch
+	 * submission errors here and propagate into subsequent ioend
+	 * submissions.
+	 */
+	list_for_each_entry_safe(ioend, next, &submit_list, io_list) {
+		int error2;
+
+		list_del_init(&ioend->io_list);
+		error2 = xfs_submit_ioend(wbc, ioend, error);
+		if (error2 && !error)
+			error = error2;
+	}
+
+	/*
+	 * We can end up here with no error and nothing to write if we race with
+	 * a partial page truncate on a sub-page block sized filesystem.
+	 */
+	if (!count)
+		end_page_writeback(page);
+done:
 	mapping_set_error(page->mapping, error);
 	return error;
 }