Re: [PATCH] block: optimize for small BS IO

[Ming Lei <ming.lei@redhat.com>]

On Tue, Oct 29, 2019 at 01:30:24PM +0900, Keith Busch wrote:
> On Tue, Oct 29, 2019 at 12:19:04PM +0800, Ming Lei wrote:
> > @@ -309,6 +309,10 @@ void __blk_queue_split(struct request_queue *q, struct bio **bio,
> >  				nr_segs);
> >  		break;
> >  	default:
> > +		if (!bio_flagged(*bio, BIO_MULTI_PAGE)) {
> > +			*nr_segs = 1;
> > +			return;
> > +		}
> >  		split = blk_bio_segment_split(q, *bio, &q->bio_split, nr_segs);
> >  		break;
> >  	}
> 
> Is there anything to gain by clearing this new flag if the result of
> blk_bio_segment_split() creates single page bio's?

That may save nothing except for one bio split for stacking devices.

thanks,
Ming