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Date: Thu, 29 Jan 2015 15:12:34 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Andrey Ryabinin <a.ryabinin@samsung.com>
Cc: linux-kernel@vger.kernel.org, Dmitry Vyukov <dvyukov@google.com>,
        Konstantin Serebryany <kcc@google.com>,
        Dmitry Chernenkov <dmitryc@google.com>,
        Andrey Konovalov <adech.fo@gmail.com>,
        Yuri Gribov <tetra2005@gmail.com>,
        Konstantin Khlebnikov <koct9i@gmail.com>,
        Sasha Levin <sasha.levin@oracle.com>, Christoph Lameter <cl@linux.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Dave Hansen <dave.hansen@intel.com>, Andi Kleen <andi@firstfloor.org>,
        x86@kernel.org, linux-mm@kvack.org, Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>
Subject: Re: [PATCH v10 04/17] mm: slub: introduce virt_to_obj function.
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On Thu, 29 Jan 2015 18:11:48 +0300 Andrey Ryabinin <a.ryabinin@samsung.com> wrote:

> virt_to_obj takes kmem_cache address, address of slab page,
> address x pointing somewhere inside slab object,
> and returns address of the begging of object.

"beginning"

The above text may as well be placed into slub_def.h as a comment.

> Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
> Acked-by: Christoph Lameter <cl@linux.com>
> ---
>  include/linux/slub_def.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
> index 9abf04e..eca3883 100644
> --- a/include/linux/slub_def.h
> +++ b/include/linux/slub_def.h
> @@ -110,4 +110,9 @@ static inline void sysfs_slab_remove(struct kmem_cache *s)
>  }
>  #endif
>  
> +static inline void *virt_to_obj(struct kmem_cache *s, void *slab_page, void *x)
> +{
> +	return x - ((x - slab_page) % s->size);
> +}

"const void *x" would be better.