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    SubjectRe: [RFC PATCH 22/22] nfs: add support for read_iter, write_iter
    Date
    On Mon, 2012-02-27 at 15:19 -0600, Dave Kleikamp wrote:
    > This patch implements the read_iter and write_iter file operations which
    > allow kernel code to initiate directIO. This allows the loop device to
    > read and write directly to the server, bypassing the page cache.
    >
    > Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
    > Cc: Zach Brown <zab@zabbo.net>
    > Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
    > Cc: linux-nfs@vger.kernel.org

    Performance is going to be absolutely terrible for O_DIRECT bvecs if you
    send just one page per RPC call. We are working on merging the O_DIRECT
    and page cache code in order to give O_DIRECT the ability to coalesce
    requests and do pNFS, and I'm hoping that code will be available soon.

    In the meantime, wouldn't it be possible to add basic coalescing to
    nfs_direct_read_schedule_bvec/nfs_direct_write_schedule_bvec more or
    less in the same way that we do for multi-page iovec segments?
    i.e. if the next bvec is contiguous with the previous, and the resulting
    RPC read length < rsize / write length < wsize, then add it to the same
    RPC call.

    --
    Trond Myklebust
    Linux NFS client maintainer

    NetApp
    Trond.Myklebust@netapp.com
    www.netapp.com

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