Swapfile creation?

I recently installed an SDD into my MacPro, and was paying attention to the storage used, both to be comfortable the SSD size was going to be enough, and also that the TM backup hard drive wouldn't fill too fast. This morning I noticed the private/var/vm folder had swapfiles totaling 64GB. My question would be how to reduce this and to understand why it happens.

I read What are the “sleepimage” and “swapfile” documents? and it warned not to delete these files. I searched some more, and found that a reboot wiped it all out. After the boot, there's one swapfile of 67MB, vs the 64 files each a full GB.

I never saw this before. I understand a reboot is the answer, but is there anything to do to prevent it occurring? I'd at least like to understand what process or app set this in motion.