linux-kernel - Re: [PATCH v2 2/2] SELinux: Increase ebitmap

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Message-ID: <51DDA8E0.4030001@tycho.nsa.gov>
Date:	Wed, 10 Jul 2013 14:33:04 -0400
From:	Stephen Smalley <sds@...ho.nsa.gov>
To:	Waiman Long <Waiman.Long@...com>
CC:	James Morris <james.l.morris@...cle.com>,
	Eric Paris <eparis@...isplace.org>,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>
Subject: Re: [PATCH v2 2/2] SELinux: Increase ebitmap_node size for 64-bit
 configuration

On 06/05/2013 05:15 PM, Waiman Long wrote:
> Currently, the ebitmap_node structure has a fixed size of 32 bytes. On
> a 32-bit system, the overhead is 8 bytes, leaving 24 bytes for being
> used as bitmaps. The overhead ratio is 1/4.
>
> On a 64-bit system, the overhead is 16 bytes. Therefore, only 16 bytes
> are left for bitmap purpose and the overhead ratio is 1/2. With a
> 3.8.2 kernel, a boot-up operation will cause the ebitmap_get_bit()
> function to be called about 9 million times. The average number of
> ebitmap_node traversal is about 3.7.
>
> This patch increases the size of the ebitmap_node structure to 64
> bytes for 64-bit system to keep the overhead ratio at 1/4. This may
> also improve performance a little bit by making node to node traversal
> less frequent (< 2) as more bits are available in each node.
>
> Signed-off-by: Waiman Long <Waiman.Long@...com>

Acked-by:  Stephen Smalley <sds@...ho.nsa.gov>

> ---
>   security/selinux/ss/ebitmap.h |    8 +++++++-
>   1 files changed, 7 insertions(+), 1 deletions(-)
>
> diff --git a/security/selinux/ss/ebitmap.h b/security/selinux/ss/ebitmap.h
> index e7eb3a9..712c8a7 100644
> --- a/security/selinux/ss/ebitmap.h
> +++ b/security/selinux/ss/ebitmap.h
> @@ -16,7 +16,13 @@
>
>   #include <net/netlabel.h>
>
> -#define EBITMAP_UNIT_NUMS	((32 - sizeof(void *) - sizeof(u32))	\
> +#ifdef CONFIG_64BIT
> +#define	EBITMAP_NODE_SIZE	64
> +#else
> +#define	EBITMAP_NODE_SIZE	32
> +#endif
> +
> +#define EBITMAP_UNIT_NUMS	((EBITMAP_NODE_SIZE-sizeof(void *)-sizeof(u32))\
>   					/ sizeof(unsigned long))
>   #define EBITMAP_UNIT_SIZE	BITS_PER_LONG
>   #define EBITMAP_SIZE		(EBITMAP_UNIT_NUMS * EBITMAP_UNIT_SIZE)
>

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