请注意，此问题仅针对linux。而到swap space，我指的是专用的swap partition。
我google在这方面做了一点，发现了这些definitions：
Paging refers to writing portions, termed pages, of a process’ memory to disk.
Swapping, strictly speaking, refers to writing the entire process, not just part, to disk.
In Linux, true swapping is exceedingly rare, but the terms paging and swapping
often are used interchangeably.
和
page-out: The system's free memory is less than a threshold "lotsfree" and unnused / least used pages are moved to the …