On Tue, May 18, 2010 at 03:40:59PM -0700, David Miller wrote: > From: Paul Mundt <lethal@xxxxxxxxxxxx> > Date: Wed, 19 May 2010 07:35:10 +0900 > > > On Tue, May 18, 2010 at 02:20:21PM -0700, David Miller wrote: > >> So one of two things should happen: > >> > >> 1) SLOB conforms to SLAB/SLUB in it's test > >> > >> 2) SLAB/SLUB conforms to SLOB in it's test > >> > >> And yes this is an either-or, you can't say they are both valid. > > > > I don't see any reason to punish SLOB for the assumptions that SLAB/SLUB > > arbitrarily took up, presumably on an architecture that should have > > specified its own alignment requirements and simply couldn't be bothered. > > Making SLAB redzoning work with arbitrary alignment is another matter > > entirely, and something that should probably be revisited. > > > > Anything that assumes more than BYTES_PER_WORD is simply broken and > > should be reverted. > > You can't make the default different in each allocator, PERIOD. > I don't disagree that having different defaults is a bit unorthodox, but that has not been a problem for any code that didn't attempt to make its own assumptions about the alignment. > If you can't know what the default is, how in the world can you know > if you need to override it? You can't. It's a guess, and you can't > say otherwise. > If an architecture requires 64-bit alignment for addressing 64-bit values on 32-bit, then that's a hard architecture requirement irrespective of whatever the slab allocator defaults to. The whole idea behind architecture minimum alignment requirements is that they are minimum requirements. > All of the CPP tests like the one used by linux/crypto.h are > ludicrious. It should absolutely be not necessary for any code to > duplicate this kind of calculation. > Agreed. > Instead, this sequence should be in linux/slab.h, and be used > universally by slab, slub, slob and anything that wants to know the > allocators alignment guarentees. > Having a slab_alignment() routine or something sounds fine, but we already have headers split out for all of the different allocators, so there's no specific reason why slob_def.h can't deviate here, too. Again, it's the crypto code that is broken for making bogus alignment assumptions in the first place. > I don't even know of a 32-bit chip outside of x86 that doesn't > potentially emit alignment requiring 64-bit memory operations for > 64-bit objects. So what SLOB is doing with a different default is > even more strange. And I bet you that even without the requirement, > x86 runs faster with 64-bit alignment of 64-bit objects. I assumed ppc32 too, but if they're really in a minority then we could also consider just inverting the logic (both x86 and ppc set HAVE_EFFICIENT_UNALIGNED_ACCESS for example). -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
