Re: [PATCH 1/4] block: setup bi_phys_segments after splitting

[Jeff Moyer <jmoyer@redhat.com>]

Ming Lei <ming.lei@canonical.com> writes:

> The number of bio->bi_phys_segments is always obtained
> during bio splitting, so it is natural to setup it
> just after bio splitting, then we can avoid to compute
> nr_segment again during merge.
>
> Signed-off-by: Ming Lei <ming.lei@canonical.com>

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>

> ---
>  block/blk-merge.c | 29 ++++++++++++++++++++++-------
>  1 file changed, 22 insertions(+), 7 deletions(-)
>
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index c4e9c37..22293fd 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -11,13 +11,16 @@
>  
>  static struct bio *blk_bio_discard_split(struct request_queue *q,
>  					 struct bio *bio,
> -					 struct bio_set *bs)
> +					 struct bio_set *bs,
> +					 unsigned *nsegs)
>  {
>  	unsigned int max_discard_sectors, granularity;
>  	int alignment;
>  	sector_t tmp;
>  	unsigned split_sectors;
>  
> +	*nsegs = 1;
> +
>  	/* Zero-sector (unknown) and one-sector granularities are the same.  */
>  	granularity = max(q->limits.discard_granularity >> 9, 1U);
>  
> @@ -51,8 +54,11 @@ static struct bio *blk_bio_discard_split(struct request_queue *q,
>  
>  static struct bio *blk_bio_write_same_split(struct request_queue *q,
>  					    struct bio *bio,
> -					    struct bio_set *bs)
> +					    struct bio_set *bs,
> +					    unsigned *nsegs)
>  {
> +	*nsegs = 1;
> +
>  	if (!q->limits.max_write_same_sectors)
>  		return NULL;
>  
> @@ -64,7 +70,8 @@ static struct bio *blk_bio_write_same_split(struct request_queue *q,
>  
>  static struct bio *blk_bio_segment_split(struct request_queue *q,
>  					 struct bio *bio,
> -					 struct bio_set *bs)
> +					 struct bio_set *bs,
> +					 unsigned *segs)
>  {
>  	struct bio_vec bv, bvprv, *bvprvp = NULL;
>  	struct bvec_iter iter;
> @@ -106,22 +113,30 @@ new_segment:
>  		sectors += bv.bv_len >> 9;
>  	}
>  
> +	*segs = nsegs;
>  	return NULL;
>  split:
> +	*segs = nsegs;
>  	return bio_split(bio, sectors, GFP_NOIO, bs);
>  }
>  
>  void blk_queue_split(struct request_queue *q, struct bio **bio,
>  		     struct bio_set *bs)
>  {
> -	struct bio *split;
> +	struct bio *split, *res;
> +	unsigned nsegs;
>  
>  	if ((*bio)->bi_rw & REQ_DISCARD)
> -		split = blk_bio_discard_split(q, *bio, bs);
> +		split = blk_bio_discard_split(q, *bio, bs, &nsegs);
>  	else if ((*bio)->bi_rw & REQ_WRITE_SAME)
> -		split = blk_bio_write_same_split(q, *bio, bs);
> +		split = blk_bio_write_same_split(q, *bio, bs, &nsegs);
>  	else
> -		split = blk_bio_segment_split(q, *bio, q->bio_split);
> +		split = blk_bio_segment_split(q, *bio, q->bio_split, &nsegs);
> +
> +	/* physical segments can be figured out during splitting */
> +	res = split ? split : *bio;
> +	res->bi_phys_segments = nsegs;
> +	bio_set_flag(res, BIO_SEG_VALID);
>  
>  	if (split) {
>  		bio_chain(split, *bio);