Configure Linux swap space with memory management and performance optimization

Check current swap configuration

First, examine your existing swap setup to understand the current state of virtual memory.

sudo swapon --show
free -h
cat /proc/swaps

If no swap is configured, the output will be empty. The free -h command shows total memory and swap usage in human-readable format.

Create a swap file

Create a dedicated swap file instead of a swap partition for more flexibility. We'll create a 2GB swap file, but adjust the size based on your system's RAM.

sudo fallocate -l 2G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile

Enable the swap file

Activate the swap file immediately and verify it's working correctly.

sudo swapon /swapfile
sudo swapon --show
free -h

You should now see the swap file listed and available swap memory in the output.

Make swap permanent

Add the swap file to /etc/fstab so it activates automatically on boot.

echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

This entry tells the system to mount the swap file at boot time with appropriate swap options.

Configure swappiness parameter

Swappiness controls how aggressively the kernel swaps memory pages to disk. The default value of 60 is often too high for desktop systems and servers with sufficient RAM.

cat /proc/sys/vm/swappiness
echo 'vm.swappiness=10' | sudo tee -a /etc/sysctl.conf

A swappiness value of 10 makes the kernel prefer keeping data in RAM and only swap when necessary. For servers with lots of RAM, consider values between 1-10.

Configure cache pressure

The vfs_cache_pressure parameter controls how aggressively the kernel reclaims memory used for caching directory and inode objects.

echo 'vm.vfs_cache_pressure=50' | sudo tee -a /etc/sysctl.conf

Setting this to 50 makes the kernel less likely to reclaim cache memory, improving filesystem performance. The default value is 100.

Apply kernel parameter changes

Reload sysctl configuration to apply the new memory management parameters without rebooting.

sudo sysctl -p
sysctl vm.swappiness vm.vfs_cache_pressure

The output should show your new parameter values are active.

Set up swap monitoring

Create a simple script to monitor swap usage and get alerts when swap usage is high.

#!/bin/bash
SWAP_USED=$(free | grep Swap | awk '{print ($3/$2)*100}')
SWAP_THRESHOLD=50

if (( $(echo "$SWAP_USED > $SWAP_THRESHOLD" | bc -l) )); then
    echo "Warning: Swap usage is ${SWAP_USED}%"
    echo "Current memory status:"
    free -h
    echo "Top memory-consuming processes:"
    ps aux --sort=-%mem | head -10
fi

sudo chmod +x /usr/local/bin/check-swap.sh

Install monitoring dependencies

Install the bc calculator for floating-point arithmetic in the monitoring script.

sudo apt update
sudo apt install -y bc

sudo dnf install -y bc

Schedule regular swap monitoring

Add a cron job to check swap usage every 15 minutes and log warnings.

echo '/15    * /usr/local/bin/check-swap.sh >> /var/log/swap-monitor.log 2>&1' | sudo crontab -

This creates a log file at /var/log/swap-monitor.log with swap usage warnings and system information.

Configure multiple swap files

For systems with high memory demands, you can create multiple swap files across different storage devices for better I/O distribution.

sudo fallocate -l 1G /swapfile2
sudo chmod 600 /swapfile2
sudo mkswap /swapfile2
sudo swapon -p 5 /swapfile2

The -p 5 option sets priority. Higher priority swap devices are used first. Add to fstab with priority:

echo '/swapfile2 none swap sw,pri=5 0 0' | sudo tee -a /etc/fstab

Monitor swap I/O performance

Use iostat to monitor swap device performance and identify I/O bottlenecks.

sudo apt install -y sysstat
iostat -x 1 5

sudo dnf install -y sysstat
iostat -x 1 5

Watch for high %iowait values during swap activity, which indicate storage bottlenecks. You can learn more about advanced I/O monitoring in our iostat and disk performance tutorial.

Tune memory overcommit settings

Configure how the kernel handles memory allocation requests that exceed available RAM plus swap.

echo 'vm.overcommit_memory=1' | sudo tee -a /etc/sysctl.conf
echo 'vm.overcommit_ratio=50' | sudo tee -a /etc/sysctl.conf
sudo sysctl -p

Setting overcommit_memory=1 allows the kernel to overcommit memory, while overcommit_ratio=50 limits overcommit to 50% of RAM plus swap space.