kernfs: Allocating memory for kernfs_iattrs with kmem_cache.

Creating a new cache for kernfs_iattrs.
Currently, memory is allocated with kzalloc() which
always gives aligned memory. On ARM, this is 64 byte aligned.
To avoid the wastage of memory in aligning the size requested,
a new cache for kernfs_iattrs is created.

Size of struct kernfs_iattrs is 80 Bytes.
On ARM, it will come in kmalloc-128 slab.
and it will come in kmalloc-192 slab if debug info is enabled.
Extra bytes taken 48 bytes.

Total number of objects created : 4096
Total saving = 48*4096 = 192 KB

After creating new slab(When debug info is enabled) :
sh-3.2# cat /proc/slabinfo
...
kernfs_iattrs_cache 4069 4096 128 32 1 : tunables 0 0 0 : slabdata 128 128 0
...

All testing has been done on ARM target.

Signed-off-by: Ayush Mittal <[e-mail]>
Signed-off-by: Vaneet Narang <[e-mail]>
Acked-by: Tejun Heo <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

fs/kernfs/dir.c

···
 			security_release_secctx(kn->iattr->ia_secdata,
 						kn->iattr->ia_secdata_len);
 		simple_xattrs_free(&kn->iattr->xattrs);
+		kmem_cache_free(kernfs_iattrs_cache, kn->iattr);
 	}
-	kfree(kn->iattr);
 	spin_lock(&kernfs_idr_lock);
 	idr_remove(&root->ino_idr, kn->id.ino);
 	spin_unlock(&kernfs_idr_lock);

fs/kernfs/inode.c

···
 	if (kn->iattr)
 		goto out_unlock;
 
-	kn->iattr = kzalloc(sizeof(struct kernfs_iattrs), GFP_KERNEL);
+	kn->iattr = kmem_cache_zalloc(kernfs_iattrs_cache, GFP_KERNEL);
 	if (!kn->iattr)
 		goto out_unlock;
 	iattrs = &kn->iattr->ia_iattr;

fs/kernfs/kernfs-internal.h

···
 }
 
 extern const struct super_operations kernfs_sops;
-extern struct kmem_cache *kernfs_node_cache;
+extern struct kmem_cache *kernfs_node_cache, *kernfs_iattrs_cache;
 
 /*
  * inode.c

fs/kernfs/mount.c

···
 
 #include "kernfs-internal.h"
 
-struct kmem_cache *kernfs_node_cache;
+struct kmem_cache *kernfs_node_cache, *kernfs_iattrs_cache;
 
 static int kernfs_sop_remount_fs(struct super_block *sb, int *flags, char *data)
 {
···
 					      0,
 					      SLAB_PANIC | SLAB_TYPESAFE_BY_RCU,
 					      NULL);
+
+	/* Creates slab cache for kernfs inode attributes */
+	kernfs_iattrs_cache  = kmem_cache_create("kernfs_iattrs_cache",
+					      sizeof(struct kernfs_iattrs),
+					      0, SLAB_PANIC, NULL);
 }