Can losetup be made efficient with sparse files?

So my setup is like this. $ truncate -s 1T volume $ losetup -f --show volume /dev/loop0 $ mkfs.ext4 /dev/loop0 $ ls -sh volume 1.1G volume $ mount /dev/loop0 /mnt/loop Now I have a 1.1TB volume, as expected. The overhead of ext4 expanded the sparse file to 1.1G, but that's fine. Now to add a file. $ dd if=/dev/urandom of=/mnt/loop/file bs=1M count=10240 $ ls -sh volume 12G volume Cool, now I don't want the file. $ rm /mnt/loop/file $ ls -sh volume 12G volume The free space is still taking up space, as expected, and $ fallocate -d volume frees up 1gb. My question is, how can I zero out the free space here without expanding the volume to the full size? $ dd if=/dev/zero will expand it to full size, and with conv=sparse makes it create a useless sparse file inside the volume. TL;DR: Is there a way to make losetup ignore writes of null blocks to null sectors, while allowing everything else?