zram

Sometimes, you don't have enough RAM to feed everything running on your computer, this often happens when you have less than 16 GB of RAM but sometimes even 16 GB isn't enough, depending on your needs. You can use swap partition/file on your drive for that, less used pages of RAM will be sent there when you don't have enough RAM, the problem is that any drive is always way slower than RAM, even the fastest SSD. Here, zram comes into play, zram is basically a swap device inside your RAM, it compresses pages sent to it so that you have more space to store data, at the cost of a bit of extra CPU usage, while still maintaining speed near to RAM speed and improving overall performance compared to a swap on disk. It is recommended to have some swap on disk too, if you're low on RAM, like 4 GB of RAM.

Prerequisite

You may not need this guide if you're running for example Garuda Linux or Fedora 33 and higher, since there's zram turned on by default. You could use some tricks from this guide like swap optimizations but Fedora for example has zram-generator preinstalled which handles zram in a different way, so you'll need to find that by yourself. To check if you have zram up and running already, type this command in terminal:

$ zramctl

Setting up GRUB

First of all, you'll need to change GRUB settings to initialize zram at boot. For that, copy & paste that command in your terminal:

$ sudo nano /etc/default/grub

Then, change the following line by adding zram.num_devices=1 at the end. For example, you will have that line in the end:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash zram.num_devices=1"

To exit editor, press "Ctrl + X", then press "Y" and then "Enter". Now, update your GRUB configuration for changes to apply:

$ sudo update-grub

Restart your computer.

Automatic zram initialization and deinitialization

Create "zram-start.sh" script for automatic zram initialization:

$ sudo nano /usr/local/bin/zram-start.sh

And then copy the following code in it while changing variable mem=8G following comment (text after "#"):

#!/bin/bash

modprobe zram num_devices=1

# Replace "8G" with the amount of your RAM in gigabytes, for example "4G", or in megabytes, for example "512M".
mem=8G

echo zstd > /sys/block/zram0/comp_algorithm
echo $mem > /sys/block/zram0/disksize
mkswap /dev/zram0
swapon -p 75 /dev/zram0

I recommend going with the size of your RAM for zram device if you're running on 16 GB of RAM and lower, and only 16 GB size of zram if you have more RAM, usually you would never need more than that. You could also not use zram at all with more than 16 GB of RAM at all, since it is slower than RAM which you have enough of, and going without swap optimizations, but with small disk swap for emergency and swappiness set from 1 to 10 to not use it until RAM is fully spent.

echo zstd sets zstd as compression algorithm for zram, it has the best comression ratio which is especially useful in low RAM conditions and also it has the best text compression which is useful while working with loads of text like in a word processor program. Other popular compression algorithms for zram are lzo-rle and lz4, lz4 has the fastest compression and decompression speed and maintains compression ratio near to lzo-rle which has some optimizations but both are inferior in compression ratio compared to zstd. In my usage, neither lzo-rle or lz4 gave any speed boost in real-life situations, neither on a slow more than a decade old PC or on a powerful machine, so zstd is the way to go here since it provides more compression which leads to more space to store data.

-p 75 sets swap priority of 75 to zram for computer to use it first until all zram devices are full, because disk swap has default priority of -2 and will not be used until zram is full. Now create "zram-stop.sh" script for automatic zram deinitialization:

$ sudo nano /usr/local/bin/zram-stop.sh

And paste following code in it:

#!/bin/bash

swapoff /dev/zram0
echo 1 > /sys/block/zram0/reset
sleep .5
modprobe -r zram

You've successfully created scripts for initialization and deinitialization of zram! A couple more steps to go.

Set-up systemd service

Firstly, allow execution of the scripts you've just made:

$ sudo chmod ugo+x /usr/local/bin/zram-start.sh

$ sudo chmod ugo+x /usr/local/bin/zram-stop.sh

Now to automatically launch zram at start-up you need to create systemd unit for it:

$ sudo systemctl edit --full --force zram.service

And paste the following in it:

[Unit]
Description=zRAM block devices swapping
[Service]
Type=oneshot
ExecStart=/usr/local/bin/zram-start.sh
ExecStop=/usr/local/bin/zram-stop.sh
RemainAfterExit=true
[Install]
WantedBy=multi-user.target

Now you need to reload systemd configuration for it to see the changes you've made:

$ sudo systemctl daemon-reload

Then start zram service and add it to start-up:

$ sudo systemctl start zram

$ sudo systemctl enable zram

Swap optimization

The last thing you need to do, open and edit "sysctl.conf":

$ sudo nano /etc/sysctl.conf

Add these lines at the end of the file:

vm.vfs_cache_pressure=500
vm.swappiness=100
vm.dirty_background_ratio=1
vm.dirty_ratio=50
vm.page-cluster=0

vm.vfs_cache_pressure=500 tells system to store less cache in your RAM.

vm.swappiness=100 sets swappiness to 100 for your system to start using zram earlier.

vm.dirty_background_ratio=1 and vm.dirty_ratio=50 controls the flow of "dirty" pages to swap.

vm.page-cluster=0 controls the number of pages up to which consecutive pages are read in from swap in a single attempt. Page cluster of 0 limits that to 1 page per attempt, which arrives lower latency.

Finish line

Just to be sure, I recommend rebooting your computer at that point. Your zram should be up and running. To check that, you can run "zramctl":

$ zramctl

Example output could be:

NAME       ALGORITHM DISKSIZE DATA COMPR TOTAL STREAMS MOUNTPOINT
/dev/zram0 zstd            8G   4K   58B    4K      12 [SWAP]