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@xxxxxxxxxxxxxxxxxxx> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
