ext4: Convert data=journal writeback to use ext4_writepages()

Add support for writeback of journalled data directly into
ext4_writepages() instead of offloading it to write_cache_pages(). This
actually significantly simplifies the code and reduces code duplication.
For checkpointing of committed data we can use ext4_writepages()
rightaway the same way as writeback of ordered data uses it on
transaction commit. For journalling of dirty mapped pages, we need to
add a special case to mpage_prepare_extent_to_map() to add all page
buffers to the journal.
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Link: https://lore.kernel.org/r/20230228051319.4085470-8-tytso@mit.edu

include/trace/events/ext4.h

@@ -584,13 +584,6 @@ DECLARE_EVENT_CLASS(ext4__page_op,
 		  (unsigned long) __entry->index)
 );
 
-DEFINE_EVENT(ext4__page_op, ext4_writepage,
-
-	TP_PROTO(struct page *page),
-
-	TP_ARGS(page)
-);
-
 DEFINE_EVENT(ext4__page_op, ext4_readpage,
 
 	TP_PROTO(struct page *page),