update_post_meta not work only when save data, not for update

[admin]

I have some trouble with regular wordpress functions in class methods
I save post meta like this and Its works fine:

public function saveMetadata( $postname ) {
    $post_id     = $_POST[ 'post_ID' ];
    $post_holder = $_POST[ $postname ];

    update_post_meta( $post_id, $postname, $post_holder );

}

But when i try update meta use same method, it doesnt work! why?

Thats i invoke this

//creation and run object
add_action( 'save_post', $quality->saveMetadata( 'project_quality' ) );