linux-kernel - Re: [PATCH] FRV: Specify the minimum slab/kmalloc alignment

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Message-Id: <20080528121535.bf766e95.akpm@linux-foundation.org>
Date:	Wed, 28 May 2008 12:15:35 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Howells <dhowells@...hat.com>
Cc:	dhowells@...hat.com, torvalds@...ux-foundation.org,
	penberg@...helsinki.fi, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] FRV: Specify the minimum slab/kmalloc alignment

On Wed, 28 May 2008 16:49:01 +0100
David Howells <dhowells@...hat.com> wrote:

> David Howells <dhowells@...hat.com> wrote:
> 
> > +#define	ARCH_KMALLOC_MINALIGN		(sizeof(long) * 2)
> > +#define	ARCH_SLAB_MINALIGN		(sizeof(long) * 2)
> 
> This doesn't work if SLAB is selected and slab debugging is enabled as these
> are passed to the preprocessor.
> 

So.. like this?

From: David Howells <dhowells@...hat.com>

Specify the minimum slab/kmalloc alignment to be 8 bytes.  This fixes a
crash when SLOB is selected as the memory allocator.  The FRV arch needs
this so that it can use the load- and store-double instructions without
faulting.  By default SLOB sets the minimum to be 4 bytes.

We need to use literal constants here as slab evaluates these within cpp.

Signed-off-by: David Howells <dhowells@...hat.com>
Cc: Pekka Enberg <penberg@...helsinki.fi>
Cc: Matt Mackall <mpm@...enic.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 include/asm-frv/mem-layout.h |    7 +++++++
 1 file changed, 7 insertions(+)

diff -puN include/asm-frv/mem-layout.h~frv-specify-the-minimum-slab-kmalloc-alignment include/asm-frv/mem-layout.h
--- a/include/asm-frv/mem-layout.h~frv-specify-the-minimum-slab-kmalloc-alignment
+++ a/include/asm-frv/mem-layout.h
@@ -31,6 +31,13 @@
 
 #define PAGE_MASK			(~(PAGE_SIZE-1))
 
+/*
+ * the slab must be aligned such that load- and store-double instructions don't
+ * fault if used
+ */
+#define	ARCH_KMALLOC_MINALIGN		8 /* (sizeof(long) * 2) */
+#define	ARCH_SLAB_MINALIGN		8 /* (sizeof(long) * 2) */
+
 /*****************************************************************************/
 /*
  * virtual memory layout from kernel's point of view
_

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