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    SubjectRe: Suggestion for O_DIRECT and friends


    On Sun, 20 Dec 1998, Rogier Wolff wrote:
    > > O_Serialized
    > > Hints the kernel that the file is read in a serial/linear way,
    > > and that caching old results isn't usefull but that Read-ahead,
    > > Read-behind and Write-clustering are.
    > >
    > > Possible usage:
    > > * tar, gzip and others
    >
    > So tar sets this flag. On my 384Mb machine, I unpack a new
    > linux-kernel when I start to compile it the whole 35Mb of linux-sources
    > has to be read back in from disk :-(
    >
    > It is all about interaction.....

    The tar (and gzip?) case is a little more complicated than I suggested:


    tar -cvf NEWARCHIVE.tar file1 file2 ...

    Here, file1 should be opened "O_ENTIRE" and the NEWARCHIVE.tar can be
    opened "O_SERIALIZED". This probably should not mean that no caching takes
    place, but if memory is at a premium (ie, there is better use for it), the
    already written .tar file can be dropped first.

    tar-xvf OLDARCHIVE.tar

    Here, an O_SERIALIZED could be used for the .tar file, but you are right,
    for the output-files, no options should be given because it is likely you
    want to use them again.

    For gzip; you know that you throw the input file away when you are done so
    caching it is useless anyway.

    Greetings,
    Arjan van de Ven



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