From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx125.postini.com [74.125.245.125]) by kanga.kvack.org (Postfix) with SMTP id CDA086B0005 for ; Tue, 5 Feb 2013 13:28:40 -0500 (EST) Message-ID: <51114F53.4030603@wwwdotorg.org> Date: Tue, 05 Feb 2013 11:28:35 -0700 From: Stephen Warren MIME-Version: 1.0 Subject: Re: next-20130204 - bisected slab problem to "slab: Common constants for kmalloc boundaries" References: <510FE051.7080107@imgtec.com> <51100E79.9080101@wwwdotorg.org> <0000013cab3780f7-5e49ef46-e41a-4ff2-88f8-46bf216d677e-000000@email.amazonses.com> In-Reply-To: <0000013cab3780f7-5e49ef46-e41a-4ff2-88f8-46bf216d677e-000000@email.amazonses.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter Cc: James Hogan , linux-next , linux-kernel , Pekka Enberg , Matt Mackall , linux-mm@kvack.org On 02/05/2013 09:36 AM, Christoph Lameter wrote: > OK I was able to reproduce it by setting ARCH_DMA_MINALIGN in slab.h. This > patch fixes it here: > > > Subject: slab: Handle ARCH_DMA_MINALIGN correctly > > A fixed KMALLOC_SHIFT_LOW does not work for arches with higher alignment > requirements. > > Determine KMALLOC_SHIFT_LOW from ARCH_DMA_MINALIGN instead. Tested-by: Stephen Warren > +/* > + * Some archs want to perform DMA into kmalloc caches and need a guaranteed > + * alignment larger than the alignment of a 64-bit integer. > + * Setting ARCH_KMALLOC_MINALIGN in arch headers allows that. > + */ > +#if defined(ARCH_DMA_MINALIGN) && ARCH_DMA_MINALIGN > 8 > +#define ARCH_KMALLOC_MINALIGN ARCH_DMA_MINALIGN > +#define KMALLOC_MIN_SIZE ARCH_DMA_MINALIGN I might be tempted to drop that #define of KMALLOC_MIN_SIZE ... > +#define KMALLOC_SHIFT_LOW ilog2(ARCH_DMA_MINALIGN) > +#else > +#define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long long) > +#endif > +#ifndef KMALLOC_MIN_SIZE > #define KMALLOC_MIN_SIZE (1 << KMALLOC_SHIFT_LOW) > #endif ... and simply drop the ifdef around that #define instead. That way, KMALLOC_MIN_SIZE is always defined in one place, and derived from KMALLOC_SHIFT_LOW; the logic will just set KMALLOC_SHIFT_LOW based on the various conditions. This seems a little safer to me; fewer conditions and less code to update if anything changes. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org