On Jun 16, 2016, at 1:20 PM, Jan Kara [off-list ref] wrote:

Well, since ext4_mb_free_metadata() is the only user of
ext4_journal_callback_add(), ext4_journal_callback_add() won't have any
user after your patch. Maybe we could just stop playing these abstraction
games nobody currently uses and just implement a helper function to add
freeing callback to the transaction list including increment of the pending
counter.

We use the journal callback for Lustre servers.  Please don't remove it.

Cheers, Andreas