Re: [PATCH V10 18/19] block: kill QUEUE_FLAG_NO_SG_MERGE

Christoph Hellwig
2018-11-16T13:58:08Z

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.
>
> Cc: Dave Chinner <dchinner@redhat.com>
> Cc: Kent Overstreet <kent.overstreet@gmail.com>
> Cc: Mike Snitzer <snitzer@redhat.com>
> Cc: dm-devel@redhat.com
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: linux-fsdevel@vger.kernel.org
> Cc: Shaohua Li <shli@kernel.org>
> Cc: linux-raid@vger.kernel.org
> Cc: linux-erofs@lists.ozlabs.org
> Cc: David Sterba <dsterba@suse.com>
> Cc: linux-btrfs@vger.kernel.org
> Cc: Darrick J. Wong <darrick.wong@oracle.com>
> Cc: linux-xfs@vger.kernel.org
> Cc: Gao Xiang <gaoxiang25@huawei.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: linux-ext4@vger.kernel.org
> Cc: Coly Li <colyli@suse.de>
> Cc: linux-bcache@vger.kernel.org
> Cc: Boaz Harrosh <ooo@electrozaur.com>
> Cc: Bob Peterson <rpeterso@redhat.com>
> Cc: cluster-devel@redhat.com
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
> block/blk-merge.c | 31 ++++++-------------------------
> block/blk-mq-debugfs.c | 1 -
> block/blk-mq.c | 3 ---
> drivers/md/dm-table.c | 13 -------------
> include/linux/blkdev.h | 1 -
> 5 files changed, 6 insertions(+), 43 deletions(-)
>
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 153a659fde74..06be298be332 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -351,8 +351,7 @@ void blk_queue_split(struct request_queue *q, struct bio **bio)
> EXPORT_SYMBOL(blk_queue_split);
>
> static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
> - struct bio *bio,
> - bool no_sg_merge)
> + struct bio *bio)
> {
> struct bio_vec bv, bvprv = { NULL };
> int cluster, prev = 0;
> @@ -379,13 +378,6 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
> nr_phys_segs = 0;
> for_each_bio(bio) {
> bio_for_each_bvec(bv, bio, iter) {
> - /*
> - * If SG merging is disabled, each bio vector is
> - * a segment
> - */
> - if (no_sg_merge)
> - goto new_segment;
> -
> if (prev && cluster) {
> if (seg_size + bv.bv_len
> > queue_max_segment_size(q))
> @@ -420,27 +412,16 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
>
> void blk_recalc_rq_segments(struct request *rq)
> {
> - bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE,
> - &rq->q->queue_flags);
> -
> - rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio,
> - no_sg_merge);
> + rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio);

Can we rename __blk_recalc_rq_segments to blk_recalc_rq_segments
can kill the old blk_recalc_rq_segments now?

Otherwise looks fine:

Reviewed-by: Christoph Hellwig <hch@lst.de>