--- linux-2.6.19/include/linux/reciprocal_div.h	1970-01-01 01:00:00.000000000 +0100
+++ linux-2.6.19-ed/include/linux/reciprocal_div.h	2006-12-04 19:01:44.000000000 +0100
@@ -0,0 +1,30 @@
+#ifndef _LINUX_RECIPROCAL_DIV_H
+#define _LINUX_RECIPROCAL_DIV_H
+
+/*
+ * Define the reciprocal value of B so that
+ * ((u32)A / (u32)B) can be replaced by :
+ * (((u64)A * RECIPROCAL_VALUE(B)) >> 32)
+ * If RECIPROCAL_VALUE(B) is precalculated, we change a divide by a multiply
+ */
+#define RECIPROCAL_VALUE(B) (u32)(((1LL << 32) + ((B) - 1))/ (B))
+
+static inline u32 reciprocal_value(unsigned int k)
+{
+	if (__builtin_constant_p(k))
+		return RECIPROCAL_VALUE(k);
+	else {
+		u64 val = (1LL << 32) + (k - 1);
+		do_div(val, k);
+		return (u32)val;
+	}
+}
+
+/*
+ * We want to avoid an expensive divide : (A / B)
+ * If B is known in advance, its reciprocal R can be precalculated/stored.
+ * then  (A / B)  =  (u32)(((u64)(A) * (R)) >> 32)
+ */
+#define RECIPROCAL_DIVIDE(A, R) (u32)(((u64)(A) * (R)) >> 32)
+
+#endif
--- linux-2.6.19/mm/slab.c	2006-12-04 11:50:19.000000000 +0100
+++ linux-2.6.19-ed/mm/slab.c	2006-12-04 19:03:42.000000000 +0100
@@ -107,6 +107,7 @@
 #include	<linux/mempolicy.h>
 #include	<linux/mutex.h>
 #include	<linux/rtmutex.h>
+#include	<linux/reciprocal_div.h>
 
 #include	<asm/uaccess.h>
 #include	<asm/cacheflush.h>
@@ -385,6 +386,7 @@ struct kmem_cache {
 	unsigned int shared;
 
 	unsigned int buffer_size;
+	unsigned int reciprocal_buffer_size;
 /* 3) touched by every alloc & free from the backend */
 	struct kmem_list3 *nodelists[MAX_NUMNODES];
 
@@ -626,10 +628,17 @@ static inline void *index_to_obj(struct 
 	return slab->s_mem + cache->buffer_size * idx;
 }
 
-static inline unsigned int obj_to_index(struct kmem_cache *cache,
-					struct slab *slab, void *obj)
+/*
+ * We want to avoid an expensive divide : (offset / cache->buffer_size)
+ *   Using the fact that buffer_size is a constant for a particular cache,
+ *   we can replace (offset / cache->buffer_size) by
+ *   RECIPROCAL_DIVIDE(offset, cache->reciprocal_buffer_size)
+ */
+static inline unsigned int obj_to_index(const struct kmem_cache *cache,
+					const struct slab *slab, void *obj)
 {
-	return (unsigned)(obj - slab->s_mem) / cache->buffer_size;
+	unsigned int offset = (obj - slab->s_mem);
+	return RECIPROCAL_DIVIDE(offset, cache->reciprocal_buffer_size);
 }
 
 /*
@@ -1400,6 +1409,8 @@ void __init kmem_cache_init(void)
 
 	cache_cache.buffer_size = ALIGN(cache_cache.buffer_size,
 					cache_line_size());
+	cache_cache.reciprocal_buffer_size =
+		reciprocal_value(cache_cache.buffer_size);
 
 	for (order = 0; order < MAX_ORDER; order++) {
 		cache_estimate(order, cache_cache.buffer_size,
@@ -2297,6 +2308,7 @@ kmem_cache_create (const char *name, siz
 	if (flags & SLAB_CACHE_DMA)
 		cachep->gfpflags |= GFP_DMA;
 	cachep->buffer_size = size;
+	cachep->reciprocal_buffer_size = reciprocal_value(size);
 
 	if (flags & CFLGS_OFF_SLAB) {
 		cachep->slabp_cache = kmem_find_general_cachep(slab_size, 0u);