This is only for ZFS. However, ZFS also does block devices, so in a typical deployment swap would be on a ZFS zvol. I'm not sure how effective this would be, t

This is only for ZFS. However, ZFS also does block devices, so in a typical deployment swap would be on a ZFS zvol. I'm not sure how effective this would be, though. If you want to 'extend' the amount of RAM you have, it would be far better to mmap() a file rather than hope that everything works as you expect with swap.