Page 64 - slides.dvi
P. 64

•
                                                                                                      •
                                                                                          •
                                                                              –
                         –
                              –
                                                                                    –
                                                                         –
               –
                                     Or
   Operating
                                                                         if
                                                                                          This
                    of
                                                                                                 page
                              for
                                                                                                      Many
                                                                    use
                                     can
                                                                                                 is
                                                                         we
                                                                              when
               select
   Systems
                    the
   —
                              each
                                                                    that
                                                                                          allows
                                                                         also
   Page
                         periodically
                                                                                    periodically
                    byte,
                                                                                                      systems
                                     extend
               lowest
                                                                                          not
                                                                    too:
                                                                                                 touched
                                                                                                               Approximating
                              page,
                                                                         have
                                                                              choosing
                                     by
                    and
                                                                              a
                         (e.g.
                                                                                    (e.g.
                                                                         a
                                                                                                      have
                              the
               value
   Replacement
                                                                                                      a
                                                      no
                                                           no
                                            yes
                                                 yes
                                                                                                               LRU
                                                                Ref?
                                                                                          recently
                    clear
                         every
                                                                              victim
                                                                                    20ms)
               page
   Algorithms
                    the
                                                                                                               (1)
                                                                         modified
                                                                              to
                                                                                          used
                                                           no
                                                 no
                                            yes
                                     maintaining
                                                      yes
               (or
                              operating
                                                                                                      reference
                                                                                    clear
                                                                         bit
                         20ms),
                                                                Dirty?
               one
                                                                                    all
                                                                                                      bit
                                     more
                                                                         (or
                                                                                          (NRU)
               of
                                                                                                      in
                                                                              replace,
                    reference
                         shift
                              system
                                            bad
                                                           best
                                                      next
                                                                         dirty
                    bit
                                                                                                      the
                         the
                                     history,
                                                                              prefer
               them)
                                                 probably
                                                                                    reference
                                                           type
                                                      best
                                                                Comment
                                                                         bit)
                                            choice
                                                                                                      PTE
               to
                                                           of
                                     e.g.
                                                                         in
                              maintains
                                                                                    bits
                                                 code
                                            for
                                                                              pages
                                                                                          replacement:
                         reference
                              an
                                                                         the
                                                 in
                                                                                                      which
                                                           page
                                                      (requires
               replace
                         bit
                                                                              with
                                                                                                      is
                                                           to
                                                 use
                              8-bit
                                                                         PTE,
                                                                                                      set
                         onto
                                                                              clear
                                                                         we
                                                                                                      by
                                            replacement
                                                           replace
                              value,
                                                      writeback)
                                                                         can
                                                                                                      h/w
                                                                              reference
                                                                         extend
                              initialized
                                                                              bits
                         most-significant
                                                                                                      whenever
                              to
                                                                         NRU
                         bit
                                                                                                      the
                                                                         to
                              zero
   60
   59   60   61   62   63   64   65   66   67   68   69