linux-kernel - Re: [PATCH V10 18/19] block: kill QUEUE_FLAG_NO_SG

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Date:   Thu, 15 Nov 2018 18:18:11 -0800
From:   Omar Sandoval <osandov@...ndov.com>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Dave Chinner <dchinner@...hat.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, Shaohua Li <shli@...nel.org>,
        linux-raid@...r.kernel.org, linux-erofs@...ts.ozlabs.org,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        linux-xfs@...r.kernel.org, Gao Xiang <gaoxiang25@...wei.com>,
        Christoph Hellwig <hch@....de>, Theodore Ts'o <tytso@....edu>,
        linux-ext4@...r.kernel.org, Coly Li <colyli@...e.de>,
        linux-bcache@...r.kernel.org, Boaz Harrosh <ooo@...ctrozaur.com>,
        Bob Peterson <rpeterso@...hat.com>, cluster-devel@...hat.com
Subject: Re: [PATCH V10 18/19] block: kill QUEUE_FLAG_NO_SG_MERGE

On Thu, Nov 15, 2018 at 04:53:05PM +0800, Ming Lei wrote:
> Since bdced438acd83ad83a6c ("block: setup bi_phys_segments after splitting"),
> physical segment number is mainly figured out in blk_queue_split() for
> fast path, and the flag of BIO_SEG_VALID is set there too.
> 
> Now only blk_recount_segments() and blk_recalc_rq_segments() use this
> flag.
> 
> Basically blk_recount_segments() is bypassed in fast path given BIO_SEG_VALID
> is set in blk_queue_split().
> 
> For another user of blk_recalc_rq_segments():
> 
> - run in partial completion branch of blk_update_request, which is an unusual case
> 
> - run in blk_cloned_rq_check_limits(), still not a big problem if the flag is killed
> since dm-rq is the only user.
> 
> Multi-page bvec is enabled now, QUEUE_FLAG_NO_SG_MERGE doesn't make sense any more.

This commit message wasn't very clear. Is it the case that
QUEUE_FLAG_NO_SG_MERGE is no longer set by any drivers?