xfs: active inodes stat is broken

vn_active only ever gets decremented, so it has a very large
negative number.  Make it track the inode count we currently have
allocated properly so we can easily track the size of the inode
cache via tools like PCP.
Signed-off-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NMark Tinguely <tinguely@sgi.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>

fs/xfs/xfs_icache.c

@@ -65,6 +65,7 @@ xfs_inode_alloc(
 		return NULL;
 	}
 
+	XFS_STATS_INC(vn_active);
 	ASSERT(atomic_read(&ip->i_pincount) == 0);
 	ASSERT(!spin_is_locked(&ip->i_flags_lock));
 	ASSERT(!xfs_isiflocked(ip));
@@ -130,6 +131,7 @@ xfs_inode_free(
 	/* asserts to verify all state is correct here */
 	ASSERT(atomic_read(&ip->i_pincount) == 0);
 	ASSERT(!xfs_isiflocked(ip));
+	XFS_STATS_DEC(vn_active);
 
 	call_rcu(&VFS_I(ip)->i_rcu, xfs_inode_free_callback);
 }

fs/xfs/xfs_super.c

@@ -1008,7 +1008,6 @@ xfs_fs_evict_inode(
 	clear_inode(inode);
 	XFS_STATS_INC(vn_rele);
 	XFS_STATS_INC(vn_remove);
-	XFS_STATS_DEC(vn_active);
 
 	xfs_inactive(ip);
 }