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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 9 May 2007 12:28:35 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/10] i386 sg: add support for chaining scatterlists

On Wed, May 09 2007, Herbert Xu wrote:
> 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.

>From a memory consumption POV, it's definitely a win to reuse the ->page
member as a pointer to the next sgtable. I didn't do that originally to
avoid complications in allocating and setting up the sg table, but I may
very well reconsider that decision soonish.

We can easily change this without disturbing the upper layers, so it's
not a big deal to change now or later.

-- 
Jens Axboe

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/