[PATCH RFC 2/2] SELinux: Increase ebitmap_node size for 64-bit configuration

[Waiman Long]

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@xxxxxx>
---
 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 922f8af..653a5b9 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)
-- 
1.7.1

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