On Wed, May 09 2007, Herbert Xu wrote:
> Jens Axboe <[email protected]> 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
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