From Brendan Gregg Scale x12 talk.
"Long before Unix supported paging, it used process swapping. While this was ok with the PDP-11/20's 64kB address spaces, it does not work as well today when address spaces can easily be hundreds of GB."
This patch disables the whole process swapping or limits it, by a system configurable setting
This new VM tunable allows limiting the swap out of whole processes, to only processes which resident size (in bytes) are equal or less than value (default value is 64KB)