Extract the function to determine the index of the slab within
the array of kmalloc caches as well as a function to determine
maximum object size from the nr of the kmalloc slab.

This is used here only to simplify slub bootstrap but will
be used later also for SLAB.

Signed-off-by: Christoph Lameter <redacted> 

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

--- linux.orig/include/linux/slab.h	2012-09-19 09:19:38.904986568 -0500
+++ linux/include/linux/slab.h	2012-09-19 09:21:27.307238804 -0500

@@ -178,6 +178,90 @@ unsigned int kmem_cache_size(struct kmem
 #endif
 
 /*
+ * Kmalloc subsystem.
+ */
+#if defined(ARCH_DMA_MINALIGN) && ARCH_DMA_MINALIGN > 8
+#define KMALLOC_MIN_SIZE ARCH_DMA_MINALIGN
+#else
+#ifdef CONFIG_SLAB
+#define KMALLOC_MIN_SIZE 32
+#else
+#define KMALLOC_MIN_SIZE 8
+#endif
+#endif
+
+#define KMALLOC_SHIFT_LOW ilog2(KMALLOC_MIN_SIZE)
+
+/*
+ * Figure out which kmalloc slab an allocation of a certain size
+ * belongs to.
+ * 0 = zero alloc
+ * 1 =  65 .. 96 bytes
+ * 2 = 120 .. 192 bytes
+ * n = 2^(n-1) .. 2^n -1
+ */
+static __always_inline int kmalloc_index(size_t size)
+{
+	if (!size)
+		return 0;
+
+	if (size <= KMALLOC_MIN_SIZE)
+		return KMALLOC_SHIFT_LOW;
+
+	if (KMALLOC_MIN_SIZE <= 32 && size > 64 && size <= 96)
+		return 1;
+	if (KMALLOC_MIN_SIZE <= 64 && size > 128 && size <= 192)
+		return 2;
+	if (size <=          8) return 3;
+	if (size <=         16) return 4;
+	if (size <=         32) return 5;
+	if (size <=         64) return 6;
+	if (size <=        128) return 7;
+	if (size <=        256) return 8;
+	if (size <=        512) return 9;
+	if (size <=       1024) return 10;
+	if (size <=   2 * 1024) return 11;
+	if (size <=   4 * 1024) return 12;
+	if (size <=   8 * 1024) return 13;
+	if (size <=  16 * 1024) return 14;
+	if (size <=  32 * 1024) return 15;
+	if (size <=  64 * 1024) return 16;
+	if (size <= 128 * 1024) return 17;
+	if (size <= 256 * 1024) return 18;
+	if (size <= 512 * 1024) return 19;
+	if (size <= 1024 * 1024) return 20;
+	if (size <=  2 * 1024 * 1024) return 21;
+	if (size <=  4 * 1024 * 1024) return 22;
+	if (size <=  8 * 1024 * 1024) return 23;
+	if (size <=  16 * 1024 * 1024) return 24;
+	if (size <=  32 * 1024 * 1024) return 26;
+	if (size <=  64 * 1024 * 1024) return 27;
+	BUG();
+
+	/* Will never be reached. Needed because the compiler may complain */
+	return -1;
+}
+