VPS normally does not have any swap space.

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sudo /bin/dd if=/dev/zero of=/var/swap.1 bs=1M count=1024
sudo /sbin/mkswap /var/swap.1
sudo chmod 600 /var/swap.1
sudo /sbin/swapon /var/swap.1
 
/etc/fstab:
/var/swap.1 swap swap defaults 0 0
 
# if it not mounted as swap, using command 
sudo /sbin/swapon /var/swap.1

swap size should be 2 times than Memory for 512MB, 1GB Memory.
Why? take Memory size 512MB for example, when 512MB is full, it will put into some of data into swap,
if now machine is sleeping, it will put 512MB into swap.
therefore, ideally swap should be 2 times than physical memory.

However, for large memory such as 16GB, swap size is based on what you need, for example, 2GB.