In-memory page states and kscand

  1. kscand task
    1. periodically sweeps through all the pages in memory
    2. notes "last access time"
      1. was accessed?
        1. increments page's age counter
      2. wasn't accessed?
        1. decrements page's age counter
      3. age counter at zero
        1. move page to inactive dirty state
In-memory page states
  1. free
    1. begin in this state
    2. not being used
    3. available for allocation, i.e. made active
  2. active
    1. allocated
    2. actively in use
  3. inactive dirty
    1. has fallen into disuse
    2. candidate for removal from main memory
  4. inactive laundered
    1. interim state
    2. contents are being moved to disk
      1. when disk I/O operation complete
        1. moved to the inactive clean state
      2. if, during the disk operation, the page is accessed
        1. moved back into the active state
  5. inactive clean
    1. laundering succeeded, i.e. contents in sync with copy on disk
    2. may be 
      1. deallocated
      2. overwritten


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