====== SWAP on Btrfs ======

SWAP on BTRFS is supported since Kernel 5.0.7.
SWAP cannot be located on snapshoted volume. The best is to create seperate volume for swap file.

Get top level ID of BTRFS:
<code>
btrfs sub list /

ID 256 gen 394 top level 5 path @
ID 258 gen 401 top level 5 path @home
...
</code>

Create non-compressed, no COW, no snapshoted swap file:
<code bash>
mkdir -p /mnt/btrfs
mount -o subvolid=5 /dev/... /mnt/btrfs
cd /mnt/btrfs
btrfs sub create @swap
cd @swap

truncate -s 0 ./swapfile
chattr +C ./swapfile
btrfs property set ./swapfile compression none

fallocate --length 8.2GB swapfile
chown root swapfile 
chmod 600 swapfile 
mkswap swapfile 
swapon swapfile
swapoff swapfile

umount /mnt/btrfs
</code>

Create mount point:
<code bash>mkdir /.swap</code>

Adapt fstab:
<file /etc/fstab>
UUID=1cf7e34b-8b09-45bd-80ae-f4658b3e0509  /.swap     btrfs    compress=none,nodatacow,noatime,subvol=@swap
/.swap/swapfile                            none	      swap     defaults
</file>

===== add resume in swap file =====

<file /etc/initramfs-tools/conf.d/resume>
RESUME=/.swap/swapfile
</file>

<code bash>update-initramfs -k all -u</code>