On 09/27/2012 12:20 AM, Christoph Lameter wrote:
> 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 <cl@xxxxxxxxx>
>
> 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;
> +}
> +
That is a bunch of branches... can't we use ilog2 for that somehow ?
In any case, you skipped "return 25".
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