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    SubjectRe: sendfile
    On Fri, 2 May 2003, Mark Mielke wrote:

    > On Fri, May 02, 2003 at 12:19:25AM -0400, Chris Friesen wrote:
    > > According to this:
    > >,39009360,39062783,00.htm
    > > using sendfile() is easier on the CPU due to less trashing of the TLB.
    > Thanks for the link. It looks quite accurate.
    > One question it raises in my mind, is whether there would be value in
    > improving write()/send() such that they detect that the userspace
    > pointer refers entirely to mmap()'d file pages, and therefore no copy
    > of data from userspace -> kernelspace should be performed. The pages
    > could be loaded and accessed directly (as they are with sendfile())
    > rather than generating a page fault to load the pages. The TLB trashing
    > does not need to occur.
    > I guess the first response to this question would be 'why not use
    > sendfile()? it already exists, and people have already begun to use
    > it...'
    > My answer is that I don't like sendfile(). It is not-yet-standard, and
    > is fairly limited. I could just be naive, but I think that:
    > write(fd, mmapped_file_pages, length);
    > Could be transparently mapped to the sendfile() code in the kernel,
    > minimizing the benefit of sendfile() having its own system call. It all
    > comes down to optimization. The current implementation of mmap() is not
    > optimal where mmap()'d file pages are passed as data to system calls.

    This is somewhat similar to what I want to do as well. As long as sendfile
    can have this, why cant we make write/send/... similar. Thus, removing the
    copy operation. Then, one can easier support streaming applications (or
    applications needing more control than sendfile)!


    > mark

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