Not Recently Used Page Replacement
Associated with each page is a reference flag such that
ref flag = 1 if the page has been referenced in recent past
-- if replacement is necessary, choose any page frame such that its
reference bit is 0. This is a page that has not been referenced in the
-- clock implementation of NRU:
last replaced pointer (lrp)
if replacement is to take place,
advance lrp to next entry (mod
table size) until one with a 0 bit
is found; this is the target for
replacement; As a side effect,
all examined PTE's have their
reference bits set to zero.
An optimization is to search for a page that is both
not recently referenced AND not dirty. Why?