pgpgin|pgpgout|pswpin|pswpout意义与差异 有大用

When ever program or data needs to be accessed and is read in from its permanent location on disk, this is called a page in request.
When ever program or data needs to be saved and is written to a permanent location on disk, this is called a page out request.

The kernel tracks each disk page (512b) read in within the pgpgin (pages paged in) counter

these counters are related to virtual memory "paging" only in the fact that they are doing disk io to load a memory page with data from disk or write the data from a memory page back to disk

 pages swapped in or out are also counted within pages paged in or out respectively since swap io is still ultimately block device based.