linux-kernel - Re: [SLUB 2/3] Large kmalloc pass through. Removal of large general slabs

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Date:	Wed, 07 Mar 2007 10:01:17 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Christoph Lameter <clameter@....com>
Cc:	akpm@...l.org, Marcelo Tosatti <marcelo@...ck.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, mpm@...enic.com,
	Manfred Spraul <manfred@...orfullife.com>
Subject: Re: [SLUB 2/3] Large kmalloc pass through. Removal of large
	general slabs

On Tue, 2007-03-06 at 18:35 -0800, Christoph Lameter wrote:
> Unlimited kmalloc size and removal of general caches >=4.
> 
> We can directly use the page allocator for all allocations 4K and larger. This
> means that no general slabs are necessary and the size of the allocation passed
> to kmalloc() can be arbitrarily large. Remove the useless general caches over 4k.
> 

> Index: linux-2.6.21-rc2-mm1/include/linux/slub_def.h
> ===================================================================
> --- linux-2.6.21-rc2-mm1.orig/include/linux/slub_def.h	2007-03-06 17:56:14.000000000 -0800
> +++ linux-2.6.21-rc2-mm1/include/linux/slub_def.h	2007-03-06 17:57:11.000000000 -0800
> @@ -55,7 +55,7 @@ struct kmem_cache {
>   */
>  #define KMALLOC_SHIFT_LOW 3
>  
> -#define KMALLOC_SHIFT_HIGH 18
> +#define KMALLOC_SHIFT_HIGH 11
>  
>  #if L1_CACHE_BYTES <= 64
>  #define KMALLOC_EXTRAS 2
> @@ -93,13 +93,6 @@ static inline int kmalloc_index(int size
>  	if (size <=  512) return 9;
>  	if (size <= 1024) return 10;
>  	if (size <= 2048) return 11;
> -	if (size <= 4096) 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;
>  	return -1;
>  }

Perhaps so something with PAGE_SIZE here, as you know there are
platforms/configs where PAGE_SIZE != 4k :-)

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