When setting up swap on Btrfs, there are a few extra things to take into consideration.

  • Must be using at least Linux Kernel 5.0
  • Must use a file
  • Must disable copy-on-write (COW)
  • Must disable compression

Create the swapfile

Create the Btrfs subvolume to hold the file. Feel free to choose whatever path you want. The reason for creating a subvolume is to avoid problems with snapshotting other volumes.

# btrfs sub create /var/swap

Create and format the file. The file must be fully allocated and not contain any holes. For the size of the file, I follow Red Hat’s recommendation of 20% of your system ram. I have 8GB of ram, which I rounded up to 2GB of swap.

# truncate -s 0 /var/swap/swapfile
# chattr +C /var/swap/swapfile
# btrfs property set /var/swap/swapfile compression none
# dd if=/dev/zero of=/var/swap/swapfile bs=1M count=2048
# chmod 600 /var/swap/swapfile
# mkswap /var/swap/swapfile

Mount it

If you have problems here, you can check dmesg for errors.

# swapon /var/swap/swapfile

Make it permanent

Add the following to /etc/fstab.

/var/swap/swapfile none swap defaults 0 0

References


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