• Create a separate swap volume (not necessary)

sudo btrfs subvolume create /mnt/btrfsbase/swap

* Add it to /etc/fstab

UUID=8f9ede3a-912f-40d6-9335-90ed3186e3e4   		      	    /swap	      	     btrfs defaults,noatime,subvol=swap	0 0

• Be sure there is no discard nor autodefrag options activated for this subvolume

• Create a swapfile

cd /swap
sudo truncate -s 0 swapfile
sudo chattr +C swapfile
btrfs property set swapfile compression none
sudo chmod 600 swapfile
sudo dd if=/dev/zero of=swapfile bs=1M count=24576 #reserve 24GB
sudo mkswap /swap/swapfile

• Find out resume device:

sudo findmnt -no UUID -T /swap/swapfile

• swap_offset command doesn't work correctly with btrfs. Download this https://github.com/osandov/osandov-linux/blob/master/scripts/btrfs_map_physical.c and compile it:

gcc -O2 -o btrfs_map_physical btrfs_map_physical.c

• Calculate offset
• Write down the last number from the output of the following command:

sudo btrfs_map_physical /swap/swapfile | head -n 2

• Result:

FILE OFFSET	FILE SIZE	EXTENT OFFSET	EXTENT TYPE	LOGICAL SIZE	LOGICAL OFFSET	PHYSICAL SIZE	DEVID	PHYSICAL OFFSET
0	134217728	0	regular	134217728	4594864128	134217728	1	4594864128

• Write down the output of the following command:

sudo getconf PAGESIZE

Result: 4096

• Calculate offset: Divide the first number under the PAGESIZE: offset = PHYSICAL_OFFSET/PAGESIZE

4594864128/4096=1121793

• Install u