> I did briefly try ZFS on my laptop a year or so ago, and it ate up half of my RAM permanently.

ZFS will use all available RAM for caching, unless you tell it otherwise (zfs_arc_max[1] or similar[2]), but it should release it when the system requires it[3].

[1]: https://docs.oracle.com/cd/E19253-01/817-0404/gjhec/index.ht...

[2]: https://www.freebsd.org/doc/handbook/zfs-advanced.html

[3]: https://superuser.com/a/1137417