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    SubjectRe: PATCH: killing read_ahead[]
    On Wed, Oct 25, 2000 at 12:30:49AM +0200, Ingo Oeser wrote:
    > On Tue, Oct 24, 2000 at 12:46:36PM -0700, Linus Torvalds wrote:
    > > Actually, the _real_ answer is to make fs/block_dev.c use the page cache
    > > instead - and generic_file_read() does read-ahead that actually improves
    > > performance, unlike the silly contortions that the direct block-dev
    > > read-ahead tries to do.
    >
    > If we had a paper about the page cache this would be easy.
    >
    > In the beginning page cache was just previously mmaped pages,
    > that are clean and ready to be mapped again.
    >
    > Today we have them either dirty or clean, mapped or not(?), with and
    > without buffers, in highmem(?) or lowmem and everybody and its
    > children is using it for everything.
    >
    > We need a clear definition about (concurrent) states of page
    > cached pages, valid transitions (and locks/sema4s to take for
    > them), assumptions, guarantees etc.
    >
    > The only thing I see guaranteed, that every big thing to be
    > cached should live there and is page aligned and page sized.
    >
    > I'm trying hard to understand a concept in the page cache and to
    > get it's limits and guarantees, but still find it hard to get
    > them.
    >
    > Time for specs, I would say ;-)
    >
    > I could help to explain and formulate, if someone could only cut
    > the edges of how it works and what it will be.
    >
    > Thanks & Regards
    >
    > Ingo Oeser
    > --
    > Feel the power of the penguin - run linux@your.pc
    > <esc>:x
    > -

    I hope we are not doing something stupid here, like breaking the
    f*!%cking page cache again. I've finaly got all the bugs out of
    NWFS on 2.4.0-test9, and have waded through the breakage of the
    past two testX releases of 2.4.

    Why do we need to disable read ahead on the page cache anyway?

    :-)

    Jeff



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