selinux: Use a kmem_cache for allocation struct file_security_struct
selinux: Use a kmem_cache for allocation struct file_security_struct

The size of struct file_security_struct is 16byte at my setup.
But, the real allocation size for per each file_security_struct
is 64bytes in my setup that kmalloc min size is 64bytes
because ARCH_DMA_MINALIGN is 64.

This allocation is called every times at file allocation(alloc_file()).
So, the total slack memory size(allocated size - request size)
is increased exponentially.

E.g) Min Kmalloc Size : 64bytes, Unit : bytes
      Allocated Size | Request Size | Slack Size | Allocation Count
    ---------------------------------------------------------------
         770048      |    192512    |   577536   |      12032

At the result, this change reduce memory usage 42bytes per each
file_security_struct

Signed-off-by: Sangwoo <55ff2da1e49d81e15ac269f4fff5057e470dde89@lge.com>
Acked-by: Stephen Smalley <d6e1285e1c84d3d5885c2124fdacc780e9fc0a94@tycho.nsa.gov>
[PM: removed extra subject prefix]
Signed-off-by: Paul Moore <88a1d58bf22a647dce58dd91f9595600dceabba9@redhat.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs