ephemeral_swap

#!/usr/bin/sudo bash
set -xeuo pipefail

# Make a Btrfs layout Qubes R4.1 installation use ephemeral swap.

dev=/dev/sda2
grub_cfg=/boot/grub2/grub.cfg  # BIOS boot
#grub_cfg=/boot/efi/EFI/qubes/grub.cfg  # EFI boot

test -e "$grub_cfg"  # sanity check 1
map=luks-$(cryptsetup luksUUID "$dev")
LC_ALL=C lsblk -dnr -o MOUNTPOINT /dev/mapper/"$map" | grep -qxF '[SWAP]'  # sanity check 2
swapoff -a
dmsetup remove --retry --force "$map"
head -c 16M /dev/random >"$dev"

bak=.bak-with-luks-swap
sed -e "s/rd.luks.uuid=$map //" -i"$bak" /etc/default/grub
sed -e "s#$map#swap                         #" -e '/ swap /s# defaults,#&discard=once,#' -i"$bak" /etc/fstab
sed -e "/$map/s#.*#swap $dev /dev/random swap,discard,sector-size=4096,cipher=aes-xts-plain64,size=512#" -i"$bak" /etc/crypttab

dracut --force --regenerate-all
grub2-mkconfig -o "$grub_cfg"

We do now have systemd > 218 (222 currently)

Thanks @jpouellet, updated - at last.