[PATCH] SELinux: add slab cache for inode security struct

Add a slab cache for the SELinux inode security struct, one of which is
allocated for every inode instantiated by the system.

The memory savings are considerable.

On 64-bit, instead of the size-128 cache, we have a slab object of 96
bytes, saving 32 bytes per object.  After booting, I see about 4000 of
these and then about 17,000 after a kernel compile.  With this patch, we
save around 530KB of kernel memory in the latter case.  On 32-bit, the
savings are about half of this.

Signed-off-by: James Morris <jmorris@namei.org>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>