Re: [RFC] SL[AUO]B common code 3/9] Extract common fields from struct kmem_cache

[Glauber Costa <glommer@parallels.com>]

On 05/15/2012 12:15 AM, Christoph Lameter wrote:
> Define "COMMON" to include definitions for fields used in all
> slab allocators. After that it will be possible to share code that
> only operates on those fields of kmem_cache.
>
> The patch basically takes the slob definition of kmem cache and
> uses the field namees for the other allocators.
>
> The slob definition of kmem_cache is moved from slob.c to slob_def.h
> so that the location of the kmem_cache definition is the same for
> all allocators.
>
> Signed-off-by: Christoph Lameter<cl@linux.com>
>
> ---
>   include/linux/slab.h     |   11 +++++++++++
>   include/linux/slab_def.h |    8 ++------
>   include/linux/slub_def.h |   11 ++++-------
>   mm/slab.c                |   30 +++++++++++++++---------------
>   mm/slob.c                |    7 -------
>   5 files changed, 32 insertions(+), 35 deletions(-)
>
> Index: linux-2.6/include/linux/slab.h
> ===================================================================
> --- linux-2.6.orig/include/linux/slab.h	2012-05-11 08:34:30.272522792 -0500
> +++ linux-2.6/include/linux/slab.h	2012-05-11 09:36:35.292445608 -0500
> @@ -93,6 +93,17 @@
>   				(unsigned long)ZERO_SIZE_PTR)
>
>   /*
> + * Common fields provided in kmem_cache by all slab allocators
> + */
> +#define SLAB_COMMON \
> +	unsigned int size, align;					\
> +	unsigned long flags;						\
> +	const char *name;						\
> +	int refcount;							\
> +	void (*ctor)(void *);						\
> +	struct list_head list;
> +
> +/*
>    * struct kmem_cache related prototypes

Isn't it better to define struct kmem_cache here, and then put the 
non-common fields under proper ifdefs ?

I myself prefer that style, but style aside, we should aim for what you
call SLAB_COMMON to encompass as many fields as we can, so the others 
will be kept to a minimum... It makes more sense, by looking from that 
angle.

> Index: linux-2.6/mm/slob.c
> ===================================================================
> --- linux-2.6.orig/mm/slob.c	2012-05-11 08:34:31.792522763 -0500
> +++ linux-2.6/mm/slob.c	2012-05-11 09:42:52.032437799 -0500
> @@ -538,13 +538,6 @@ size_t ksize(const void *block)
>   }
>   EXPORT_SYMBOL(ksize);
>
> -struct kmem_cache {
> -	unsigned int size, align;
> -	unsigned long flags;
> -	const char *name;
> -	void (*ctor)(void *);
> -};
> -

Who defines struct kmem_cache for the slob now ?

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