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    SubjectRe: [RFC PATCH 22/22] nfs: add support for read_iter, write_iter
    On 02/27/2012 04:08 PM, Myklebust, Trond wrote:
    > 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.

    I basically followed the example of what the block layer was doing, but
    coalescing makes more sense for nfs. I'll rework it to do that.

    Thanks,
    Shaggy


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