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: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick 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
@@ -863,12 +870,12 @@ 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);
 
 	/*
@@ -884,22 +891,14 @@ xfs_writepage_map(
 		if (error2 && !error)
 			error = error2;
 	}
-	} else if (error) {
-		xfs_aops_discard_page(page);
-		ClearPageUptodate(page);
-		unlock_page(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.
+	 * 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.
 	 */
-		clear_page_dirty_for_io(page);
-		set_page_writeback(page);
-		unlock_page(page);
+	if (!count)
 		end_page_writeback(page);
-	}
-
+done:
 	mapping_set_error(page->mapping, error);
 	return error;
 }