Is there a fundamental reason that ext4 *can't* or *shouldn't* support inline data with 128-byte inodes? As far as I can tell, the kernel ext4 implementation only allows inline data with 256-byte or larger inodes, because it requires the system.data xattr to exist, even if the actual data requires 60 bytes or less. (The implementation in debugfs, on the other hand, handles inline data in 128-byte inodes just fine. And it seems like it'd be fairly straightforward to change the kernel implementation to support it as well.) For filesystems that don't need to store xattrs in general, and can live with the other limitations of 128-byte inodes, using a 128-byte inode can save substantial space compared to a 256-byte inode (many megabytes worth of inode tables, versus 4k for each file between 61-160 bytes), and many small files or small directories would still fit in 60 bytes.
