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Date: Tue, 21 Nov 2023 08:49:45 -0700
From: Keith Busch <kbusch@kernel.org>
To: Ming Lei <ming.lei@redhat.com>
Cc: Keith Busch <kbusch@meta.com>, linux-block@vger.kernel.org,
	linux-nvme@lists.infradead.org, io-uring@vger.kernel.org,
	axboe@kernel.dk, hch@lst.de, joshi.k@samsung.com,
	martin.petersen@oracle.com
Subject: Re: [PATCHv3 1/5] bvec: introduce multi-page bvec iterating
Message-ID: <ZVzRmQ66yRDJWMiZ@kbusch-mbp>
References: <20231120224058.2750705-1-kbusch@meta.com>
 <20231120224058.2750705-2-kbusch@meta.com>
 <ZVxsLYj9oH+j3RQ8@fedora>
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In-Reply-To: <ZVxsLYj9oH+j3RQ8@fedora>

On Tue, Nov 21, 2023 at 04:37:01PM +0800, Ming Lei wrote:
> On Mon, Nov 20, 2023 at 02:40:54PM -0800, Keith Busch wrote:
> > From: Keith Busch <kbusch@kernel.org>
> > 
> > Some bio_vec iterators can handle physically contiguous memory and have
> > no need to split bvec consideration on page boundaries.
> 
> Then I am wondering why this helper is needed, and you can use each bvec
> directly, which is supposed to be physically contiguous.

It's just a helper function to iterate a generic bvec.
 
> > diff --git a/include/linux/bvec.h b/include/linux/bvec.h
> > index 555aae5448ae4..9364c258513e0 100644
> > --- a/include/linux/bvec.h
> > +++ b/include/linux/bvec.h
> > @@ -184,6 +184,12 @@ static inline void bvec_iter_advance_single(const struct bio_vec *bv,
> >  		((bvl = bvec_iter_bvec((bio_vec), (iter))), 1);	\
> >  	     bvec_iter_advance_single((bio_vec), &(iter), (bvl).bv_len))
> >  
> > +#define for_each_mp_bvec(bvl, bio_vec, iter, start)			\
> > +	for (iter = (start);						\
> > +	     (iter).bi_size &&						\
> > +		((bvl = mp_bvec_iter_bvec((bio_vec), (iter))), 1);	\
> > +	     bvec_iter_advance_single((bio_vec), &(iter), (bvl).bv_len))
> > +
> 
> We already have bio_for_each_bvec() to iterate over (multipage)bvecs
> from bio.

Right, but we are not dealing with a bio here. We have a bip bvec
instead, so can't use bio_for_each_bvec().