linux-kernel - Re: [PATCH 13/13] block: don't check for BIO_MAX_PAGES in blk_bio_segment

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Message-ID: <20170502102223.GB1803@ming.t460p>
Date:   Tue, 2 May 2017 18:22:24 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     NeilBrown <neilb@...e.com>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        Ming Lei <tom.leiming@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/13] block: don't check for BIO_MAX_PAGES in
 blk_bio_segment_split()

On Tue, May 02, 2017 at 01:42:26PM +1000, NeilBrown wrote:
> blk_bio_segment_split() makes sure bios have no more than
> BIO_MAX_PAGES entries in the bi_io_vec.
> This was done because bio_clone_bioset() (when given a
> mempool bioset) could not handle larger io_vecs.
> 
> No driver uses bio_clone_bioset() any more, they all
> use bio_clone_fast() if anything, and bio_clone_fast()
> doesn't clone the bi_io_vec.

Maybe in future, some drivers still may try to use 
bio_clone_bioset() again, I suggest to add some comments
on bio_clone_bioset() to make this usage explicitly. Also
better to trigger a warning if a big src bio is passed to
bio_clone_bioset().

Thanks,
Ming