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Date:   Wed, 21 Nov 2018 09:46:08 +0100
From:   Christoph Hellwig <>
To:     Sagi Grimberg <>
Cc:     Ming Lei <>, Christoph Hellwig <>,
        Jens Axboe <>,,,,
        Dave Chinner <>,
        Kent Overstreet <>,
        Mike Snitzer <>,,
        Alexander Viro <>,, Shaohua Li <>,,,
        David Sterba <>,,
        "Darrick J . Wong" <>,, Gao Xiang <>,
        Theodore Ts'o <>,,
        Coly Li <>,,
        Boaz Harrosh <>,
        Bob Peterson <>,
Subject: Re: [PATCH V10 09/19] block: introduce bio_bvecs()

On Tue, Nov 20, 2018 at 09:35:07PM -0800, Sagi Grimberg wrote:
>> Given it is over TCP, I guess it should be doable for you to preallocate one
>> 256-bvec table in one page for each request, then sets the max segment size as
>> (unsigned int)-1, and max segment number as 256, the preallocated table
>> should work anytime.
> 256 bvec table is really a lot to preallocate, especially when its not
> needed, I can easily initialize the bvec_iter on the bio bvec. If this
> involves preallocation of the worst-case than I don't consider this to
> be an improvement.

Ok, I took a look at the nvme-tcp code and it seems you care about
bios because you want a contiguos bio chunk for sending it down
the networking code.  Yes, in that case we sort of need to iterate
over bios.  But you already have a special case for discard, so you
don't really need any of the magic in the bio_bvecs() helper either
can can just count bi_vcnt in the bio.

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