When we truncate existing items in the tree log we've been searching for
each individual item and removing them.  This is unnecessary churn and
searching, just keep track of the slot we are on and how many items we need
to delete and delete them all at once.  Thanks,

(speaking of unnecessary churn :))

+next_slot:
 		path->slots[0]--;
+
 		btrfs_item_key_to_cpu(path->nodes[0], &found_key,
 				      path->slots[0]);
 
 		if (found_key.objectid != objectid)
 			break;
 
-		ret = btrfs_del_item(trans, log, path);
+		start_slot = path->slots[0];
+		del_nr++;
+		if (start_slot)
+			goto next_slot;

A linear backwards scan?  Of potentially 64k leaves?

Can you use bin_search() to look for the first key >= [objectid,0,0] in
the leaf?  And probably a single comparison of slot 0 to fast path the
case where the whole leaf contains the object id?

+		ret = btrfs_del_items(trans, log, path, start_slot, del_nr);
 		if (ret)
 			break;
 		btrfs_release_path(path);
 	}
+	if (!ret && del_nr)
+		ret = btrfs_del_items(trans, log, path, start_slot, del_nr);
 	btrfs_release_path(path);

You shouldn't have to duplicate deletion and releasing the path if you
wrap the calculation of start_slot and nr in a helper.  Something like:

	nr = find_nr_and_slot_doo_de_doo(, &start_slot);
	if (nr > 0)
		btrfs_del_items(, start_slot, nr);

- z