> I'm not sure I understand, wouldn't the filesystem need to be involved > at some level? How can the block layer differentiate lazilly discarded data > blocks from ones that are still in use without the aid of the > filesystem?
It might be me that doesn't understand. Yes, the filesystem is involved. Current linux filesystems can trim on demand or using fstrim. That mechanism seems to be like it should suffice if exposed in the most common cases.
