Security: smack: replace kzalloc with kmem_cache for inode_smack

The patch use kmem_cache to allocate/free inode_smack since they are
alloced in high volumes making it a perfect case for kmem_cache.

As per analysis, 24 bytes of memory is wasted per allocation due
to internal fragmentation. With kmem_cache, this can be avoided.

Accounting of memory allocation is below :
 total       slack            net      count-alloc/free        caller
Before (with kzalloc)
1919872      719952          1919872      29998/0          new_inode_smack+0x14

After (with kmem_cache)
1201680          0           1201680      30042/0          new_inode_smack+0x18

>From above data, we found that 719952 bytes(~700 KB) of memory is
saved on allocation of 29998 smack inodes.

Signed-off-by: Rohit <rohit.kr@samsung.com>

security/smack/smack_lsm.c

@@ -53,6 +53,7 @@
 #define SMK_SENDING	2
 
 LIST_HEAD(smk_ipv6_port_list);
+static struct kmem_cache *smack_inode_cache;
 
 #ifdef CONFIG_SECURITY_SMACK_BRINGUP
 static void smk_bu_mode(int mode, char *s)
@@ -240,7 +241,7 @@ struct inode_smack *new_inode_smack(struct smack_known *skp)
 {
 	struct inode_smack *isp;
 
-	isp = kzalloc(sizeof(struct inode_smack), GFP_NOFS);
+	isp = kmem_cache_zalloc(smack_inode_cache, GFP_NOFS);
 	if (isp == NULL)
 		return NULL;
 
@@ -767,7 +768,7 @@ static int smack_inode_alloc_security(struct inode *inode)
  */
 static void smack_inode_free_security(struct inode *inode)
 {
-	kfree(inode->i_security);
+	kmem_cache_free(smack_inode_cache, inode->i_security);
 	inode->i_security = NULL;
 }
 
@@ -4265,10 +4266,16 @@ static __init int smack_init(void)
 	if (!security_module_enable(&smack_ops))
 		return 0;
 
+	smack_inode_cache = KMEM_CACHE(inode_smack, 0);
+	if (!smack_inode_cache)
+		return -ENOMEM;
+
 	tsp = new_task_smack(&smack_known_floor, &smack_known_floor,
 				GFP_KERNEL);
-	if (tsp == NULL)
+	if (tsp == NULL) {
+		kmem_cache_destroy(smack_inode_cache);
 		return -ENOMEM;
+	}
 
 	printk(KERN_INFO "Smack:  Initializing.\n");