[PATCH v4 0/13] ext4: Stop using ext4_writepage() for writeout of ordered data

[Jan Kara <jack@suse.cz>]

Hello,

this patch series modifies ext4 so that we stop using ext4_writepage() for
writeout of ordered data during transaction commit (through
generic_writepages() from jbd2_journal_submit_inode_data_buffers()). Instead we
directly call ext4_writepages() from the
ext4_journal_submit_inode_data_buffers(). This is part of Christoph's effort
to get rid of the .writepage() callback in all filesystems.

I have also modified ext4_writepages() to use write_cache_pages() instead of
generic_writepages() so now we don't expose .writepage hook at all. We still
keep ext4_writepage() as a callback for write_cache_pages(). We should refactor
that path as well and get rid of ext4_writepage() completely but that is for a
separate cleanup. Also note that jbd2 still uses generic_writepages() in its
jbd2_journal_submit_inode_data_buffers() helper because it is still used from
OCFS2. Again, something to be dealt with in a separate patchset.

Changes since v3:
* Added export of buffer_migrate_page_norefs()
* Clarified commit message about page migration a bit

Changes since v2:
* Added Reviewed-by tags from Christoph
* Added WARN_ON to verify we're not trying to start transaction from
  transaction commit writeback
* Converted fastcommit path to use ext4_writepages() for data writeout
* Some minor tweaks suggested by Christoph

Changes since v1:
* Added Reviewed-by tags from Ritesh
* Added patch to get rid of generic_writepages() in ext4_writepages()
* Added patch to get rid of .writepage hook

								Honza
Previous versions:
Link: http://lore.kernel.org/r/20221130162435.2324-1-jack@suse.cz # v1
Link: http://lore.kernel.org/r/20221202163815.22928-1-jack@suse.cz # v2
Link: http://lore.kernel.org/r/20221205122604.25994-1-jack@suse.cz # v3