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    SubjectHow to find out which pages were copied-on-write?
    Hi,

    in an application that MAP_PRIVATEly mmap()s a file it would
    be quite helpful for me to find out which pages have been
    copied-on-write.

    I found that mincore() does a similar thing by reporting which
    pages are currently residing in physical memory, but what
    I want to know is which pages differ from the original file
    image on disk.

    Can you recommend a way to do that? (does not need to be
    portable beyond Linux)

    Alternatively, it would be sufficient if I could turn
    a private mapping into a shared one (and possibly do an
    msync() afterwards if I need to make sure the changes
    have been written out). Would such a feature need a
    lot of effort to implement?


    Yet another feature that I could use if it were available:
    A "copy-on-read"-mapping. There, a page would become a private
    copy of a process once _another_ process wrote data to the
    corresponding file location. But I suspect that feature
    could be very hard to implement...

    Regards,

    Lutz Vieweg


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