The third field, which indicates any recent activity, is used to determine which pages
show the most processing activity, and which are relatively inactive. This information
is used by several page-swapping policy schemes to determine which pages should
73Demand Paging
Operating System
1
(figure 3.5)
Demand paging requires
that the Page Map Table
for each job keep track of
each page as it is loaded
or removed from main
memory. Each PMT tracks
the status of the page,
whether it has been
modified, whether it has
been recently referenced,
and the page frame
number for each page
currently in main memory.
(Note: For this illustration,
the Page Map Tables have
been simplified. See Table
3.3 for more detail.)
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remain in main memory and which should be swapped out when the system needs to
make room for other pages being requested.