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    SubjectRe: PATCH: Raw device IO for 2.1.131
    > Date: Tue, 15 Dec 1998 19:40:28 -0800 (PST)
    > From: Linus Torvalds <>
    > I'm not arguing against zero-copy per se. I'm arguing against
    > people who think memory management tricks are a good idea. They
    > generally aren't, look at where Mach is.
    > Ok ok ok, as usual you are the voice of reason.
    > Just one situation I want clarified, do you think we'll be able to fit
    > into our framework a way to (for example) get at the user's
    > application level headers during a write (ie. http header, then the
    > data)?

    Another thing which rawio helps with, but could be implemented separately,
    is a way how to hint the kernel that this data won't be needed again.
    Currently, a couple of tasks are like that, e.g. burning a CD, playing large
    mpegs, etc. In all these cases, current kernel behaves badly, as it has no
    way of knowing which buffers and pages to keep in buffer/page caches and which
    to throw out, so it results in all caches being filled with useless data and
    preciously cached data being thrown away. Here even sendfile won't help, as
    it caches the things.
    Rawio helps here, as it does not leave the things in caches at all, but one
    could cope with special hints in open and either throw those pages
    immediately, or mark them so that they'll be freed up the first time someone
    asks for a page/buffer.

    Jakub Jelinek | |
    Administrator of SunSITE Czech Republic, MFF, Charles University
    UltraLinux | |
    Linux version 2.1.130 on a sparc64 machine (3958.37 BogoMips)

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