> I'm confused. I thought the active list contained pages that were in use,
> and the inactive ones that weren't. Thus how does anything other than the
> actual user of pages make this change?
>

Before the page daemon can move pages from active to inactive list,
there is a separate process (page marking process) whose job is to
mark pages based on the aging criterion  (LRU algorithm). The page
marking happens first, then the page daemon only moves pages which
have been marked. However, if the page is locked, that page is
skipped.

Thus, between two arrivals of the page daemon, the page marking
process needs to execute.