I used this procedure to add swap space to a server, where I not more available partitions, but had space on a previously formated partition.

# mkdir /var/swap

Create container files:
# dd if=/dev/zero of=/var/swap/swapfile1 bs=1024 count=65536
# dd if=/dev/zero of=/var/swap/swapfile2 bs=1024 count=65536
# dd if=/dev/zero of=/var/swap/swapfile3 bs=1024 count=65536
# dd if=/dev/zero of=/var/swap/swapfile4 bs=1024 count=65536

Format as swap:
# mkswap /var/swap/swapfile1
# mkswap /var/swap/swapfile2
# mkswap /var/swap/swapfile3
# mkswap /var/swap/swapfile4

Add them to startup:
# vi /etc/fstab
…
/var/swap/swapfile1 swap swap defaults 0 0
/var/swap/swapfile2 swap swap defaults 0 0
/var/swap/swapfile3 swap swap defaults 0 0
/var/swap/swapfile4 swap swap defaults 0 0
…

Enable them:
# swapon -a
Check them:
# swapon -sh