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    SubjectRe: mmap/munmap semantics
    On Wed, 23 Feb 2000, Benjamin C.R. LaHaise wrote:

    > On Wed, 23 Feb 2000, Richard Guenther wrote:
    >
    > > So how can I throw away a dirty (shared) mapping of a file without
    > > generating disk io? Remember, I do not care about the contents of the file
    > > at the mmap place.
    > > A possible solution would be to be able to convert a shared mapping to
    > > a private one? If I'm the only user of the shared mapping (so its a
    > > virtually private one) this should be easy - just "disconnect" it. In the
    > > other case I do not really know how to handle this.
    >
    > The most portable and easiest way to achieve this behaviour right now is
    > to use individual files or shm segments for the shared mappings. Using
    > SysV shared memory will get you the most performance since it won't get
    > written back to disk early (like mmaped files). If that doesn't give you
    > enough space, I strongly recommend using 1 file per shared "segment",
    > since the semantics you get by truncating and then extending the mapping
    > are exactly what you want. As a bonus, this technique works on
    > filesystems that don't support files with holes =)

    Yes, but unfortunately the individual file approach does not work in case
    we (ideally) want to operate on a whole disk...

    Richard.


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