The Jargon File (version 4.4.7, 29 Dec 2003):

page in
 v.

    [MIT]

    1. To become aware of one's surroundings again after having paged out (see
    page out). Usually confined to the sarcastic comment: ?Eric pages in, 
    film at 11!?

    2. Syn. swap in; see swap.


The Free On-line Dictionary of Computing (30 December 2018):

page in

    What a paging system does when it
   copies part of a task's working memory from swap space
   on disk to RAM.

   [Jargon File]

   (1995-01-23)