linux-kernel - Re: [RFC] SLUB - define OO_ macro instead of hardcoded numbers

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Date:	Wed, 22 Oct 2008 21:01:01 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Cyrill Gorcunov <gorcunov@...il.com>
CC:	Christoph Lameter <cl@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] SLUB - define OO_ macro instead of hardcoded numbers

Cyrill Gorcunov wrote:
> Something like that?
> 
> 		- Cyrill -
> ---
> 
>  mm/slub.c |   18 +++++++++++-------
>  1 file changed, 11 insertions(+), 7 deletions(-)
> 
> Index: linux-2.6.git/mm/slub.c
> ===================================================================
> --- linux-2.6.git.orig/mm/slub.c	2008-10-22 21:11:26.000000000 +0400
> +++ linux-2.6.git/mm/slub.c	2008-10-22 21:57:11.000000000 +0400
> @@ -153,6 +153,10 @@
>  #define ARCH_SLAB_MINALIGN __alignof__(unsigned long long)
>  #endif
>  
> +#define OO_SHIFT	16
> +#define OO_MASK		((1 << OO_SHIFT) - 1)
> +#define MAX_OBJS_PER_PAGE	65535 /* see struct page.objects */
> +
>  /* Internal SLUB flags */
>  #define __OBJECT_POISON		0x80000000 /* Poison object */
>  #define __SYSFS_ADD_DEFERRED	0x40000000 /* Not yet visible via sysfs */
> @@ -290,7 +294,7 @@ static inline struct kmem_cache_order_ob
>  						unsigned long size)
>  {
>  	struct kmem_cache_order_objects x = {
> -		(order << 16) + (PAGE_SIZE << order) / size
> +		(order << OO_SHIFT) + (PAGE_SIZE << order) / size
>  	};
>  
>  	return x;
> @@ -298,12 +302,12 @@ static inline struct kmem_cache_order_ob
>  
>  static inline int oo_order(struct kmem_cache_order_objects x)
>  {
> -	return x.x >> 16;
> +	return x.x >> OO_SHIFT;
>  }
>  
>  static inline int oo_objects(struct kmem_cache_order_objects x)
>  {
> -	return x.x & ((1 << 16) - 1);
> +	return x.x & OO_MASK;
>  }
>  
>  #ifdef CONFIG_SLUB_DEBUG
> @@ -764,8 +768,8 @@ static int on_freelist(struct kmem_cache
>  	}
>  
>  	max_objects = (PAGE_SIZE << compound_order(page)) / s->size;
> -	if (max_objects > 65535)
> -		max_objects = 65535;
> +	if (max_objects > MAX_OBJS_PER_PAGE)
> +		max_objects = MAX_OBJS_PER_PAGE;
>  
>  	if (page->objects != max_objects) {
>  		slab_err(s, page, "Wrong number of objects. Found %d but "
> @@ -1819,8 +1823,8 @@ static inline int slab_order(int size, i
>  	int rem;
>  	int min_order = slub_min_order;
>  
> -	if ((PAGE_SIZE << min_order) / size > 65535)
> -		return get_order(size * 65535) - 1;
> +	if ((PAGE_SIZE << min_order) / size > MAX_OBJS_PER_PAGE)
> +		return get_order(size * MAX_OBJS_PER_PAGE) - 1;
>  
>  	for (order = max(min_order,
>  				fls(min_objects * size - 1) - PAGE_SHIFT);

Looks good to me. If Christoph ACKs this, please send me a proper patch 
with your sign-off and I'll merge it to slab.git.

		Pekka
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