sudo swapon -s
Example setting/resetting swapfile to 6GB. Note that while multiple swap files can exist, when hibernating to disk only one swap file is being used.
sudo swapoff /swapfile
sudo dd if=/dev/zero of=/swapfile count=1k bs=6M
sudo mkswap /swapfile
sudo chown root:root /swapfile
sudo chmod 600 /swapfile
sudo swapon /swapfile