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    SubjectRe: [RFC PATCH] fs/direct-io.c: Set bi_rw when alloc bio.
    Date
    majianpeng <majianpeng@gmail.com> writes:

    > On 2012-07-27 22:21 Jeff Moyer <jmoyer@redhat.com> Wrote:
    >>majianpeng <majianpeng@gmail.com> writes:
    >>
    >>> When exec bio_alloc, the bi_rw is zero.But after calling bio_add_page,
    >>> it will use bi_rw.
    >>> Fox example, in functiion __bio_add_page,it will call merge_bvec_fn().
    >>> The merge_bvec_fn of raid456 will use the bi_rw to judge the merge.
    >>>>> if ((bvm->bi_rw & 1) == WRITE)
    >>>>> return biovec->bv_len; /* always allow writes to be mergeable */
    >>>
    >>> Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
    >>
    >>Good catch. How did you find this? Did you experience data corruption
    >>as a result of this oversight, reduced performance due to missed merge
    >>opportunities, or did you just notice it in reviewing the code?
    >>
    >>Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
    >>
    > Sorry for late to reply. When i analysed the performance of raid5, i found this bug.

    OK, thanks. In the future, it would be good to include that information
    in the patch description.

    Cheers,
    Jeff


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