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    SubjectRe: [PATCH V10 17/19] block: don't use bio->bi_vcnt to figure out segment number
    On Thu, Nov 15, 2018 at 06:11:40PM -0800, Omar Sandoval wrote:
    > On Thu, Nov 15, 2018 at 04:53:04PM +0800, Ming Lei wrote:
    > > It is wrong to use bio->bi_vcnt to figure out how many segments
    > > there are in the bio even though CLONED flag isn't set on this bio,
    > > because this bio may be splitted or advanced.
    > >
    > > So always use bio_segments() in blk_recount_segments(), and it shouldn't
    > > cause any performance loss now because the physical segment number is figured
    > > out in blk_queue_split() and BIO_SEG_VALID is set meantime since
    > > bdced438acd83ad83a6c ("block: setup bi_phys_segments after splitting").
    > >
    > > Cc: Dave Chinner <dchinner@redhat.com>
    > > Cc: Kent Overstreet <kent.overstreet@gmail.com>
    > > Fixes: 7f60dcaaf91 ("block: blk-merge: fix blk_recount_segments()")
    >
    > From what I can tell, the problem was originally introduced by
    > 76d8137a3113 ("blk-merge: recaculate segment if it isn't less than max segments")
    >
    > Is that right?

    Indeed, will update it in next version.

    Thanks,
    Ming

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