linux-kernel - Re: [BUG] SLOB breaks Crypto

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Message-ID: <1274224575.11603.1248.camel@calx>
Date:	Tue, 18 May 2010 18:16:15 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	David Miller <davem@...emloft.net>
Cc:	lethal@...ux-sh.org, penberg@...helsinki.fi,
	herbert@...dor.apana.org.au, ken@...elabs.ch, geert@...ux-m68k.org,
	michael-dev@...i-braun.de, linux-kernel@...r.kernel.org,
	linux-crypto@...r.kernel.org, anemo@....ocn.ne.jp
Subject: Re: [BUG] SLOB breaks Crypto

On Tue, 2010-05-18 at 15:40 -0700, David Miller wrote:
> 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.
> 
> 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.

Agreed. However, every arch should -also- set ARCH_KMALLOC_MINALIGN
appropriately so that we have documentation of the hardware requirements
on each platform.

> 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.

No doubt but SLOB explicitly trades faster for smaller.

-- 
Mathematics is the supreme nostalgia of our time.


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