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    SubjectRe: [PATCH 00/17] md: cleanup on direct access to bvec table
    Hi Shaohua,

    On Fri, Feb 17, 2017 at 6:16 AM, Shaohua Li <shli@kernel.org> wrote:
    > On Thu, Feb 16, 2017 at 07:45:30PM +0800, Ming Lei wrote:
    >> In MD's resync I/O path, there are lots of direct access to bio's
    >> bvec table. This patchset kills most of them, and the conversion
    >> is quite straightforward.
    >
    > I don't like this approach. The MD uses a hacky way to manage pages allocated,
    > this is the root of the problem. The patches add another hack way to do the

    Yes, I agree, and bio_iov_iter_get_pages() uses this kind of hacky way too
    actually.

    > management. I'd like to see explict management of the pages, for example, add
    > data structure in r1bio to manage the pages, then we can use existing API for
    > all the stuffes we need.

    Yeah, that is definitely clean, but we have to pay the following cost:

    - allocate at least N * (128 + 4) bytes per each r1_bio/r10_bio
    - N is pool_info.raid_disks for raid1, and conf->copies for raid10

    If we are happy to introduce the cost, I can take this way in V1.


    Thanks,
    Ming Lei

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