ext4: make data=journal support large block size

ext4: make data=journal support large block size

Currently, ext4_set_inode_mapping_order() does not set max folio order
for files with the data journalling flag. For files that already have
large folios enabled, ext4_inode_journal_mode() ignores the data
journalling flag once max folio order is set.

This is not because data journalling cannot work with large folios, but
because credit estimates will go through the roof if there are too many
blocks per folio.

Since the real constraint is blocks-per-folio, to support data=journal
under LBS, we now set max folio order to be equal to min folio order for
files with the journalling flag. When LBS is disabled, the max folio order
remains unset as before.

Therefore, before ext4_change_inode_journal_flag() switches the journalling
mode, we call truncate_pagecache() to drop all page cache for that inode,
and filemap_write_and_wait() is called unconditionally.

After that, once the journalling mode has been switched, we can safely
reset the inode mapping order, and the mapping_large_folio_support() check
in ext4_inode_journal_mode() can be removed.

Suggested-by: Jan Kara <jack@suse.cz>
Suggested-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Message-ID: <20251121090654.631996-22-libaokun@huaweicloud.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>