Things change or an overestimation may happen.
To reduce the swap space portion backed by disk:
Verify that disk-based swap is not in use (blocks == free):
# swap -l
swapfile dev swaplo blocks free
/dev/zvol/dsk/rpool/swap 256,1 16 62914544 62914544
Remove the swap device from the VMM:
# swap -d /dev/zvol/dsk/rpool/swap
Confirm the old device is gone:
# swap -l
No swap devices configured
Reduce the size or create a smaller ZFS volume for the new swap device:
# zfs destroy rpool/swap
# zfs create -V 4G -b $(pagesize) rpool/swap
# zfs set primarycache=metadata rpool/swap
Add the swap device to the VMM:
# swap -a /dev/zvol/dsk/rpool/swap
Verify the new disk-based swap info:
# swap -l
swapfile dev swaplo blocks free
/dev/zvol/dsk/rpool/swap 256,1 16 8388592 8388592
Note that we may have to invert the order of operations.
That is, begin by adding a new (smaller) device and then remove the old (larger) device.
In any case, don't forget to adjust changes accordingly in /etc/vfstab.
