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Beyond Physical Memory: Policies In a virtual memory manager, life is easy when you have a lot
 

Summary: 21
Beyond Physical Memory: Policies
In a virtual memory manager, life is easy when you have a lot
of free memory. A page fault occurs, you find a free page on the
free-page list, and assign it to the faulting page. Hey, Operating
System, congratulations! You did it again.
Unfortunately, things get a little more interesting when lit-
tle memory is free. In such a case, this memory pressure forces
the OS to start paging out pages to make room for actively-used
pages. Deciding which page (or pages) to evict is encapsulated
within the replacement policy of the OS; historically, it was one
of the most important decisions the early virtual memory sys-
tems made, as older systems had little physical memory. Min-
imally, it is an interesting set of policies worth knowing a little
more about. And thus our problem:
THE CRUX: HOW TO DECIDE WHICH PAGE TO EVICT
How can the OS decide which page (or pages) to evict from
memory? This decision is made by the replacement policy of
the system, which usually follows some general principles (dis-
cussed below) but also includes certain tweaks to avoid corner-

  

Source: Arpaci-Dusseau, Remzi - Department of Computer Sciences, Department of Computer Sciences, University of Wisconsin at Madison

 

Collections: Computer Technologies and Information Sciences