# Using SWAP in the Linux system

In limited memory environments, creating a swap file would make the system load more applications, but the performance may degrade due to the overhead of swapping between physical and virtual memory.

Check the swap stat

show swap list

swapon --show

Using Disk space

Create a swap and mount it

sudo fallocate -l 8G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon --priority 1 /swapfile

# persistent
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab
# 10 minimal, 60 default, 100 max
sudo sysctl -w vm.swappiness=60

Tip

Persistant the sysctl setting, can use drop-in configuration in /etc/sysctl.d/

Stop swap and delete it

sudo swapoff /swapfile
sudo rm /swapfile

# remove line from /etc/fstab
sudo vim /etc/fstab

Using ZRAM

Check kernel

lsmod | grep zram

# if not present, switch it on
sudo modprobe zram num_devices=1

Install (Debian)

sudo apt update
sudo apt install zram-config

Configuare

Setup zram size, half of mahcine ram in this case.

echo $(( $(grep MemTotal /proc/meminfo | awk '{print $2}') * 1024 / 2 )) | sudo tee /sys/block/zram0/disksize

Switch on

sudo mkswap /dev/zram0

# Manual start
sudo swapon /dev/zram0

# Auto start
sudo systemctl enable zram-config
sudo systemctl start zram-config

Switch off

sudo systemctl stop zram-config

Test the swap

install stress

sudo apt install stress

using stress to test the Swap usage.

# 4 process, 2GB each for 60 seconds
stress --vm 4 --vm-bytes 2G --timeout 60s