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    SubjectRe: [PATCH] O_STREAMING - flag for optimal streaming I/O
    On Thu Oct 10, 2002 at 10:33:36AM +0200, Giuliano Pochini wrote:
    > On 10-Oct-2002 Erik Andersen wrote:
    > > I don't think grep is a very good candidate for O_STREAMING. I
    > > usually want the stuff I grep to stay in cache. O_STREAMING is
    > > much better suited to applications like ogle, vlc, xine, xmovie,
    > > xmms etc since there is little reason for the OS to cache things
    > > like songs and movies you aren't likely to hear/see again any
    > > time soon.
    > The kernel already have cache pruning algorithm. O_STREAMING logic
    > should not clear caches if there is no need to do that. We could

    The entire point of O_STREAMING is to let user space specify
    policy. If user space user space knows with 100% certainty that
    the data being read/written from a particular file descriptor is
    use-once-and-discard data, then it makes sense to honor that
    hint. In this case, user space knows best and can set policy on
    a per file descriptor basis.

    Note that most applications do not want to use this flag. But
    for a few applications it just just perfect. For example, if I
    am playing a DVD there is absolutely no point in the kernel
    trying to cache the content of the DVD. A DVD has way too much
    content for caching it to do any good, and since most people
    watch a DVD once through from beginning to end, there is no point
    stuffing the DVD's content into the pagecache, thereby crowding
    out other things that should remain in cache.


    Erik B. Andersen
    --This message was written using 73% post-consumer electrons--
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