Does a pager move or copy a page when handling a page fault?

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When a process accesses a page not in the main memory but in the swap space, a page fault happens, and the pager reads a page from swap space to main memory.



Is the read a move or copy? In other words, is there still a copy of the page in the swap space?



If it is a copy, does it mean that the pager has to update the copy in the swap space whenever there is a change to the copy of the page in the main space?



Thanks.



Operating System Concepts says:




  1. We find a free frame (by taking one from the free-frame list, for example).


  2. We schedule a disk operation to read the desired page into the newly allocated frame.




and this figure also shows copies of some pages (A, C and F) are in both swap space and main memory, and no page only exists in main memory but not in swap space:



enter image description here






linux virtual-memory







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    When a process accesses a page not in the main memory but in the swap space, a page fault happens, and the pager reads a page from swap space to main memory.



    Is the read a move or copy? In other words, is there still a copy of the page in the swap space?



    If it is a copy, does it mean that the pager has to update the copy in the swap space whenever there is a change to the copy of the page in the main space?



    Thanks.



    Operating System Concepts says:




    1. We find a free frame (by taking one from the free-frame list, for example).


    2. We schedule a disk operation to read the desired page into the newly allocated frame.




    and this figure also shows copies of some pages (A, C and F) are in both swap space and main memory, and no page only exists in main memory but not in swap space:



    enter image description here






    linux virtual-memory







    share|improve this question























      up vote
      0
      down vote

      favorite









      up vote
      0
      down vote

      favorite











      When a process accesses a page not in the main memory but in the swap space, a page fault happens, and the pager reads a page from swap space to main memory.



      Is the read a move or copy? In other words, is there still a copy of the page in the swap space?



      If it is a copy, does it mean that the pager has to update the copy in the swap space whenever there is a change to the copy of the page in the main space?



      Thanks.



      Operating System Concepts says:




      1. We find a free frame (by taking one from the free-frame list, for example).


      2. We schedule a disk operation to read the desired page into the newly allocated frame.




      and this figure also shows copies of some pages (A, C and F) are in both swap space and main memory, and no page only exists in main memory but not in swap space:



      enter image description here






      linux virtual-memory







      share|improve this question













      When a process accesses a page not in the main memory but in the swap space, a page fault happens, and the pager reads a page from swap space to main memory.



      Is the read a move or copy? In other words, is there still a copy of the page in the swap space?



      If it is a copy, does it mean that the pager has to update the copy in the swap space whenever there is a change to the copy of the page in the main space?



      Thanks.



      Operating System Concepts says:




      1. We find a free frame (by taking one from the free-frame list, for example).


      2. We schedule a disk operation to read the desired page into the newly allocated frame.




      and this figure also shows copies of some pages (A, C and F) are in both swap space and main memory, and no page only exists in main memory but not in swap space:



      enter image description here






      linux virtual-memory




      linux virtual-memory






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      asked 36 mins ago









      Tim

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