A page-in does not necessarily represent a page being recoverd from the swap area. It could be an executable code that is being paged in from a file system or could be a copy-on-write page being duplicated. Both of which are of normal occourences that do not necessarily indicate a shortage of memory. On the other hand page-out always represent data being forcibly ejected by the kernel. As I said, you can check further through $> top or vmstat -S 5.

This is the fact of the field... Since I haven't yet read the your book, I cannot comment on the implications.

Sam