Re: [PATCH 1/4] block: use ARCH_KMALLOC_MINALIGN as the default dma pad mask

FUJITA Tomonori
2008-05-20T09:59:04Z

On Tue, 20 May 2008 02:52:31 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Tue, 20 May 2008 17:38:20 +0800 Herbert Xu <herbert@gondor.apana.org.au> wrote:
>
> > On Tue, May 20, 2008 at 02:31:29AM -0700, Andrew Morton wrote:
> > >
> > > So here you're using it for "dma aligment" whereas crypto is using it
> > > (or ARCH_SLAB_MINALIGN!) for "cpu 64-bit alignment".
> >
> > No the 64-bit alignment is just an example. The purpose of
> > CRYPTO_MINALIGN is pretty much the same as ARCH_KMALLOC_MINALIGN,
> > i.e., the minimum alignment guaranteed by kmalloc. The only
> > reason it exists is because ARCH_KMALLOC_MINALIGN isn't defined
> > on all platforms.
>
> I'm struggling to understand what you're saying here.
>
> The comment you have there over the CRYPTO_MINALIGN definition is quite
> specific. Is it wrong?
>
> Whether the mapping between CRYPTO_MINALIGN and ARCH_KMALLOC_MINALIGN
> is abusive is (I find) hard to say, because first one would need to be
> able to say what ARCH_KMALLOC_MINALIGN is for. I expect it was for DMA
> purposes.

Yeah, ARCH_KMALLOC_MINALIGN is for DMA. Non coherent platforms define
it.