What do you do to pages?

• If the page is dirty, you have to write it out to disk.

  • record the disk block number for the page in the PTE.

• If the page is clean, you don’t have to do anything.

  • just overwrite the page with new data
  • make sure you know where the old copy of the page came from

• Want to avoid THRASHING

  • When a paging algorithm breaks down
  • Most of the OS time spent in ferrying pages to and from disk
  • no time spent doing useful work.
  • the system is OVERCOMMITTED
    • no idea what pages should be resident in order to run effectively
  • Solutions include:
    • SWAP
    • Buy more memory

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