I implemented zstd compression in btrfs/squashfs, and work on upstream zstd.

* Btrfs compression is multithreaded, and can use up to the number of cores available on the system. * Compression might not help speed on SSDs, but it should help reduce the burn rate, if you care about that. * My intern wrote a patch to add compression level support to zstd in btrfs [1]. It should be merged upstream soon. * Slightly off topic, but grub will soon understand btrfs compressed with zstd.

[1] https://lore.kernel.org/linux-btrfs/20181031181108.289340-1-...