Re: [PATCH] slob: push the min alignment to long long

On Wed, 22 Jun 2011, David Rientjes wrote:

quoted

  * struct kmem_cache
  *
  * manages a cache.

Looks like we lost some valuable information in the comments when this got
moved to slab.h :(

Ok. If we want a description for these defines then lets use this.


Subject: slab allocators: Provide generic description of alignment defines

Provide description for alignment defines.

Signed-off-by: Christoph Lameter <redacted>

---
 include/linux/slab.h |   10 ++++++++++
 1 file changed, 10 insertions(+)

Index: linux-2.6/include/linux/slab.h
===================================================================

--- linux-2.6.orig/include/linux/slab.h	2011-06-23 09:26:55.000000000 -0500
+++ linux-2.6/include/linux/slab.h	2011-06-23 09:33:46.000000000 -0500

@@ -133,12 +133,22 @@ unsigned int kmem_cache_size(struct kmem
 #define KMALLOC_MAX_SIZE	(1UL << KMALLOC_SHIFT_HIGH)
 #define KMALLOC_MAX_ORDER	(KMALLOC_SHIFT_HIGH - PAGE_SHIFT)

+/*
+ * 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.
+ */
 #ifdef ARCH_DMA_MINALIGN
 #define ARCH_KMALLOC_MINALIGN ARCH_DMA_MINALIGN
 #else
 #define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long long)
 #endif

+/*
+ * Setting ARCH_SLAB_MINALIGN in arch headers allows a different alignment.
+ * Intended for arches that get misalignment faults even for 64 bit integer
+ * aligned buffers.
+ */
 #ifndef ARCH_SLAB_MINALIGN
 #define ARCH_SLAB_MINALIGN __alignof__(unsigned long long)
 #endif

--

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