Re: [PATCH 07/10] crypto: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN

Herbert Xu
2022-04-17T08:08:58Z

On Fri, Apr 15, 2022 at 01:38:15PM +0200, Ard Biesheuvel wrote:
>
> If this is the case, things are already broken today. We never take
> ARCH_DMA_MINALIGN into account when adding the driver ctx size to the
> overall allocation size.

No it's not broken because kmalloc guarantees alignment. For
example, if ARCH_DMA_MINALIGN is 128 bytes, then kmalloc will
always return a pointer that's 128-byte aligned. That guarantees
this object and the next object are on different cache-lines.

If you reduce the kmalloc minimum alignment to 64 bytes, then
the two neighbouring objects can share cache-lines, even if
each object is bigger than 128 bytes (e.g., if they were 192
bytes each).

Cheers,
--
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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