Hi Christoph,
On Thu, Jan 10, 2013 at 4:14 PM, Christoph Lameter <cl@xxxxxxxxx> wrote:
> Standardize the constants that describe the smallest and largest
> object kept in the kmalloc arrays for SLAB and SLUB.
>
> Differentiate between the maximum size for which a slab cache is used
> (KMALLOC_MAX_CACHE_SIZE) and the maximum allocatable size
> (KMALLOC_MAX_SIZE, KMALLOC_MAX_ORDER).
>
> Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>
>
> Index: linux/include/linux/slab.h
> ===================================================================
> --- linux.orig/include/linux/slab.h 2013-01-10 09:42:25.640301677 -0600
> +++ linux/include/linux/slab.h 2013-01-10 09:43:40.857456229 -0600
> @@ -163,7 +163,12 @@ struct kmem_cache {
> #else /* CONFIG_SLOB */
>
> /*
> - * The largest kmalloc size supported by the slab allocators is
> + * Kmalloc array related definitions
> + */
> +
> +#ifdef CONFIG_SLAB
> +/*
> + * The largest kmalloc size supported by the SLAB allocators is
> * 32 megabyte (2^25) or the maximum allocatable page order if that is
> * less than 32 MB.
> *
> @@ -173,9 +178,24 @@ struct kmem_cache {
> */
> #define KMALLOC_SHIFT_HIGH ((MAX_ORDER + PAGE_SHIFT - 1) <= 25 ? \
> (MAX_ORDER + PAGE_SHIFT - 1) : 25)
> +#define KMALLOC_SHIFT_MAX KMALLOC_SHIFT_HIGH
> +#define KMALLOC_SHIFT_LOW 5
> +#else
> +/*
> + * SLUB allocates up to order 2 pages directly and otherwise
> + * passes the request to the page allocator.
> + */
> +#define KMALLOC_SHIFT_HIGH (PAGE_SHIFT + 1)
> +#define KMALLOC_SHIFT_MAX (MAX_ORDER + PAGE_SHIFT)
> +#define KMALLOC_SHIFT_LOW 3
> +#endif
>
Why do we need to distinguish SLAB from SLUB here?
I mean: why do we need to maintain 32 bytes as the smallest kmalloc cache?
Thanks,
--
Ezequiel
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