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    SubjectRe: [RFC PATCH 02/17] block: simplify bio_add_page()
    On Mon, Dec 22, 2014 at 12:48:29PM +0100, Dongsu Park wrote:
    > From: Kent Overstreet <kmo@daterainc.com>
    >
    > Since generic_make_request() can now handle arbitrary size bios, all we
    > have to do is make sure the bvec array doesn't overflow.
    > __bio_add_page() doesn't need to call ->merge_bvec_fn(), where
    > we can get rid of unnecessary code paths.

    This needs an explanation of why removign the call to ->merge_bvec_fn
    is fine for bio_add_pc_page. I guess it's because neither
    the target pscsi pass through mode, nor the osd code ever use anything
    but a simple scsi devices that doesn't even have one, but it needs to be
    clearly spelled out.

    > + * Attempt to add a page to the bio_vec maplist. This will only fail if
    > + * bio->bi_vcnt == bio->bi_max_vecs.

    It also fails on a cloned bio, although that might better be turned into
    a BUG_ON().



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