linux-kernel - Re: [PATCH 7/10] i386 sg: add support for chaining scatterlists

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Message-Id: <E1Hlj17-0001CJ-00@gondolin.me.apana.org.au>
Date:	Wed, 09 May 2007 20:03:29 +1000
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	jens.axboe@...cle.com (Jens Axboe)
Cc:	linux-kernel@...r.kernel.org, jens.axboe@...cle.com
Subject: Re: [PATCH 7/10] i386 sg: add support for chaining scatterlists

Jens Axboe <jens.axboe@...cle.com> wrote:
> 
> diff --git a/include/asm-i386/scatterlist.h b/include/asm-i386/scatterlist.h
> index d7e45a8..794b68c 100644
> --- a/include/asm-i386/scatterlist.h
> +++ b/include/asm-i386/scatterlist.h
> @@ -8,8 +8,11 @@ struct scatterlist {
>     unsigned int       offset;
>     dma_addr_t         dma_address;
>     unsigned int       length;
> +    struct scatterlist *next;
> };

BTW, the crypto layer's scatterlist already has a chaining mechanism
using the existing structure.  The only difference is that the chained
pointer is stored inside the 'struct page *' rather than a new pointer.
Its existence is flagged by a zero value in the length field.

Now I'm not super-religious about this but we should at least consider
whether forking out 4 bytes in every scatterlist member is worthwhile
investment when we can use 12 bytes at the end instead.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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