linux-kernel - Re: [dm-devel] [PATCH v3 02/26] block: Convert integrity to bvec_alloc

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Message-ID: <20121002210006.GS26488@google.com>
Date:	Tue, 2 Oct 2012 14:00:06 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, axboe@...nel.dk,
	"Martin K. Petersen" <martin.petersen@...cle.com>, tj@...nel.org
Subject: Re: [dm-devel] [PATCH v3 02/26] block: Convert integrity to
 bvec_alloc_bs()

On Tue, Oct 02, 2012 at 11:37:37AM -0400, Vivek Goyal wrote:
> On Mon, Sep 24, 2012 at 03:34:42PM -0700, Kent Overstreet wrote:
> 
> [..]
> >  /**
> >   * bio_integrity_alloc - Allocate integrity payload and attach it to bio
> >   * @bio:	bio to attach integrity metadata to
> > @@ -84,37 +47,39 @@ struct bio_integrity_payload *bio_integrity_alloc(struct bio *bio,
> >  						  unsigned int nr_vecs)
> >  {
> >  	struct bio_integrity_payload *bip;
> > -	unsigned int idx = vecs_to_idx(nr_vecs);
> >  	struct bio_set *bs = bio->bi_pool;
> > +	unsigned long idx = BIO_POOL_NONE;
> > +	unsigned inline_vecs;
> > +
> > +	if (!bs) {
> > +		bip = kmalloc(sizeof(struct bio_integrity_payload) +
> > +			      sizeof(struct bio_vec) * nr_vecs, gfp_mask);
> > +		inline_vecs = nr_vecs;
> > +	} else {
> > +		bip = mempool_alloc(bs->bio_integrity_pool, gfp_mask);
> > +		inline_vecs = BIP_INLINE_VECS;
> > +	}
> >  
> > -	if (!bs)
> > -		bs = fs_bio_set;
> 
> Ok, this is change of behavior. Previously we will fall back to fs_bio_set
> and now you do kmalloc. This change looks to be independent of bip_vec
> pointer. Can you please break it out in a separate patch and also explain
> that how does this change help.

I'm not sure it's worth breaking out into a separate patch, but I
definitely should've mentioned it in the patch description.

It just didn't make sense to be using fs_bio_set if a bio_set wasn't
specified before - if a bio set wasn't specified we're still using
kmalloc for the bio_integrity_payload, so we're not protected from
memory allocation failures and it doesn't buy us anything.

All it does is introduce the possibility of deadlock, if we weren't
supposed to be using fs_bio_set for whatever reason.
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