ext4: Clear dirty bit from pages without data to write

With journalled data it can happen that checkpointing code will write
out page contents without clearing the page dirty bit. The logic in
ext4_page_nomap_can_writeout() then results in us never calling
mpage_submit_page() and thus clearing the dirty bit. Drop the
optimization with ext4_page_nomap_can_writeout() and just always call to
mpage_submit_page(). ext4_bio_write_page() knows when to redirty the
page and the additional clearing & setting of page dirty bit for ordered
mode writeout is not that expensive to jump through the hoops for it.

Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230329154950.19720-4-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/inode.c

@@ -2348,19 +2348,6 @@ static int ext4_da_writepages_trans_blocks(struct inode *inode)
 				MAX_WRITEPAGES_EXTENT_LEN + bpp - 1, bpp);
 }
 
-/* Return true if the folio needs to be written as part of transaction commit */
-static bool ext4_folio_nomap_can_writeout(struct folio *folio)
-{
-	struct buffer_head *bh, *head;
-
-	bh = head = folio_buffers(folio);
-	do {
-		if (buffer_dirty(bh) && buffer_mapped(bh) && !buffer_delay(bh))
-			return true;
-	} while ((bh = bh->b_this_page) != head);
-	return false;
-}
-
 static int ext4_journal_page_buffers(handle_t *handle, struct page *page,
 				     int len)
 {
@@ -2545,13 +2532,11 @@ static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd)
 			 * range operations before discarding the page cache.
 			 */
 			if (!mpd->can_map) {
-				if (ext4_folio_nomap_can_writeout(folio)) {
-					WARN_ON_ONCE(sb->s_writers.frozen ==
-						     SB_FREEZE_COMPLETE);
-					err = mpage_submit_folio(mpd, folio);
-					if (err < 0)
-						goto out;
-				}
+				WARN_ON_ONCE(sb->s_writers.frozen ==
+					     SB_FREEZE_COMPLETE);
+				err = mpage_submit_folio(mpd, folio);
+				if (err < 0)
+					goto out;
 				/* Pending dirtying of journalled data? */
 				if (folio_test_checked(folio)) {
 					WARN_ON_ONCE(sb->s_writers.frozen >=