dphys-swapfile binary package in Ubuntu Bionic amd64

 This init.d script exists so one does not need to have a fixed size
 swap partition. Instead install without swap partition and then run this,
 with file size (re-)computed automatically to fit the current RAM size.
 .
 By default (and hence on installation) it creates swapfile twice as
 big as the present RAM amount with an upper limit of 2 GB.
 .
 It's also very helpful when included in SD card, USB stick or disk
 images which are distributed and run on many machines with different
 amount of RAM, e.g. different models of the Raspberry Pi or cloud
 images.

Source package