Introduction
What is zram? How to use it? Please see this related guide:
One of the main drawbacks to zram is its incompatibility with hibernation.
For this and other reasons zram users may wish to create an additional ‘backing’ SWAP device.
For quick-install steps skip to this section.
Creating a swap file
SWAP is a subject all its own, so for our purposes we will focus on the example of a swap file.
The ArchWiki has a handy introduction here:
https://wiki.archlinux.org/title/Swap#Swap_file
Instructions
Or follow the guide here.
Click to show
The first consideration is what size for the swap.
In order to ensure hibernation is successful even during the heaviest workloads it is advisable to make swap the size of your available RAM and zram combined.
Click to show calculation command
This bash string should calculate your total available ram, zram size, add them, and round up to the nearest whole number.
_hibned=$(awk "BEGIN {print $(zramctl | tail -1 | awk -F '[^0-9]*' '{ print $3 }')+$(awk '/MemTotal/ { printf "%.3f \n", $2/1024/1024 }' /proc/meminfo); exit}"); printf "%.0f\n" "$_hibned"
With this size in mind we can now create the swap file. We will assume 16gb here.
sudo mkswap -U clear --size 16G --file /swapfile
We will also want to add this swap to our /etc/fstab file.
The line should look like this. Note the priority. It should be lower than your zram priority.
/swapfile none swap defaults,pri=0 0 0
After creating your backing swap file and adding it to /etc/fstab it is time to reboot!
Hibernation will now be possible while zram is used for SWAP.
Another word about priority
If you followed this guide and the zram guide then the priorities should already be acceptable.
The intention is to make sure that zram has a higher priority than the backing swap device. In the given example zram should have a priority of 100 and our /swapfile should have a priority of 0.
This ensures that during general operation the system will make use of the more performant zram and, because systemd automatically disregards zram while hibernating, the otherwise ignored /swapfile will be used for hibernation.
Quick Install
If you just want a few commands then these are for you.
Click to show
printf '\nFinding optimal swapfile size.\n'; _hibned=$(awk "BEGIN {print $(zramctl | tail -1 | awk -F '[^0-9]*' '{ print $3 }')+$(awk '/MemTotal/ { printf "%.3f \n", $2/1024/1024 }' /proc/meminfo); exit}"); _roundhibned=$(printf "%.0f\n" "$_hibned"); printf "\n%s""$_roundhibned"" GB\n\n"
printf '\nCreating swap file.\n\n'; sudo mkswap -U clear --size "$_roundhibned"G --file /swapfile; printf '\nDone.\n\n'
printf '\nAdding line to /etc/fstab.\n\n'; if [ "$(tail -c1 /etc/fstab; printf x)" != $'\nx' ]; then printf "\n" | sudo tee -a /etc/fstab; fi; printf '/swapfile none swap defaults,pri=0 0 0\n' | sudo tee -a /etc/fstab; printf '\nDone.\n\nTime to REBOOT.\n\n'
Hibernation
Hibernation may require extra configuration.
In the case of a swap file, as is used the the examples above, refer to this guide:
[HowTo] Configure hibernation with a swap file
More Information
ArchWiki swapfile-zram hibernation page
Power management/Suspend and hibernate - ArchWiki