Swap Management: When and How to Use Swap

System is using excessive swap causing performance degradation, or swap is missing on a VPS causing OOM kills on memory pressure.

Check swap usage, tune swappiness, and create a swap file when needed.

# Check swap usage
free -h
swapon --show

# Create a 4GB swap file
fallocate -l 4G /swapfile
chmod 600 /swapfile
mkswap /swapfile
swapon /swapfile

# Verify
free -h

# Persist across reboots in /etc/fstab
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

# Tune swappiness (0-100, default 60)
# Lower = prefer RAM, higher = prefer swap
sysctl vm.swappiness=10          # for a database server
echo 'vm.swappiness=10' >> /etc/sysctl.conf

# Check cache pressure
sysctl vm.vfs_cache_pressure

# Disable swap temporarily
swapoff /swapfile

# Show processes using swap (approximate)
for pid in /proc/[0-9]*/status; do
  awk '/VmSwap/{print $2" "FILENAME}' $pid
done | sort -rn | head

Swap prevents OOM kills at the cost of IO latency. vm.swappiness=10 means the kernel will avoid swapping until absolutely necessary — good for database servers where latency matters more than memory efficiency.