linux-kernel - Re: [PATCH v5 11/12] block: Add bio_clone

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Message-ID: <20120809025610.GK7262@moria.home.lan>
Date:	Wed, 8 Aug 2012 19:56:10 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, axboe@...nel.dk, agk@...hat.com,
	neilb@...e.de, drbd-dev@...ts.linbit.com, vgoyal@...hat.com,
	mpatocka@...hat.com, sage@...dream.net, yehuda@...newdream.net
Subject: Re: [PATCH v5 11/12] block: Add bio_clone_bioset()

On Wed, Aug 08, 2012 at 04:21:20PM -0700, Tejun Heo wrote:
> On Mon, Aug 06, 2012 at 03:08:40PM -0700, Kent Overstreet wrote:
> > This consolidates some code, and will help in a later patch changing how
> > bio cloning works.
> 
> I think it would be better to introduce bio_clone*() functions in a
> separate patch and convert the users in a different one.
> 
> >  /**
> > - *	bio_clone	-	clone a bio
> > + *	bio_clone_bioset -	clone a bio
> >   *	@bio: bio to clone
> >   *	@gfp_mask: allocation priority
> > + *	@bs: bio_set to allocate from
> >   *
> >   * 	Like __bio_clone, only also allocates the returned bio
> >   */
> > -struct bio *bio_clone(struct bio *bio, gfp_t gfp_mask)
> > +struct bio *bio_clone_bioset(struct bio *bio, gfp_t gfp_mask,
> > +			     struct bio_set *bs)
> >  {
> > -	struct bio *b = bio_alloc(gfp_mask, bio->bi_max_vecs);
> > +	struct bio *b = bio_alloc_bioset(gfp_mask, bio->bi_max_vecs, bs);
> >  
> >  	if (!b)
> >  		return NULL;
> > @@ -485,7 +487,7 @@ struct bio *bio_clone(struct bio *bio, gfp_t gfp_mask)
> >  	if (bio_integrity(bio)) {
> >  		int ret;
> >  
> > -		ret = bio_integrity_clone(b, bio, gfp_mask, fs_bio_set);
> > +		ret = bio_integrity_clone(b, bio, gfp_mask, bs);
> >  
> >  		if (ret < 0) {
> >  			bio_put(b);
> > @@ -495,6 +497,12 @@ struct bio *bio_clone(struct bio *bio, gfp_t gfp_mask)
> >  
> >  	return b;
> >  }
> > +EXPORT_SYMBOL(bio_clone_bioset);
> > +
> > +struct bio *bio_clone(struct bio *bio, gfp_t gfp_mask)
> > +{
> > +	return bio_clone_bioset(bio, gfp_mask, fs_bio_set);
> > +}
> 
> So, bio_clone() loses its function comment.  Also, does it even make
> sense to call bio_clone() from fs_bio_set?

I'll re add the function comment if you want, just for a single line
wrapper I don't know if it's worth the cost - comments get out of date,
and they're more stuff to wade through.

> Let's say it's so, then
> what's the difference from using _kmalloc variant?

bio_kmalloc() fails if nr_iovecs > 1024, bio_alloc_bioset() fails if
nr_iovecs > 256

and bio_alloc_bioset() is mempool backed, bio_kmalloc() is not.

AFAICT that's it.
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