linux-kernel - Re: [PATCH next] bio: zero inlined bio

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Message-ID: <20081223113938.GJ32491@kernel.dk>
Date:	Tue, 23 Dec 2008 12:39:38 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH next] bio: zero inlined bio_vec

On Tue, Dec 23 2008, Hugh Dickins wrote:
> On Tue, 23 Dec 2008, Jens Axboe wrote:
> > On Tue, Dec 23 2008, Jens Axboe wrote:
> > > 
> > > That is, it iterates *bio_orig but indexes bio since it knows it has the
> > > same number of segments. So this code is the odd one out, I'd be
> > > surprised if we had more such cases. And since it would be nice to get
> > > rid of the need to memset in general, can you try with the below patch?
> > 
> > Nope, that still wont be enough, since we leave entries 0..i-1
> > uninitialized. Lets just do this instead.
> 
> Yes, that second version worked for me.  But if __blk_queue_bounce()
> is indeed the odd one out (likely but not certain), then the extension
> below makes more sense - I don't like how your bio.c returns a cleared
> bio_vec in some cases but not in others.  This is running fine for me
> on my test machines, but my test coverage is probably very poor (am I
> ever using more than the inlined bio_vec?), and I've not really tried
> to understand all the ways through bvec_alloc_bs().
> 
> Hugh
> 
> --- a/fs/bio.c
> +++ b/fs/bio.c
> @@ -180,7 +180,7 @@ struct bio_vec *bvec_alloc_bs(gfp_t gfp_
>  	 * kzalloc() for the exact number of vecs right away.
>  	 */
>  	if (!bs)
> -		bvl = kzalloc(nr * sizeof(struct bio_vec), gfp_mask);
> +		bvl = kmalloc(nr * sizeof(struct bio_vec), gfp_mask);
>  
>  	/*
>  	 * see comment near bvec_array define!
> @@ -237,9 +237,6 @@ fallback:
>  		}
>  	}
>  
> -	if (bvl)
> -		memset(bvl, 0, bvec_nr_vecs(*idx) * sizeof(struct bio_vec));
> -
>  	return bvl;
>  }

I agree, those should be killed too. It's why I didn't want to rely on
memset for fixing your issue :-)

I'll merge the bounce.c fix into the original patch.

-- 
Jens Axboe

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