refresh sharepoint parent modal dialog on closing child popup

I have a button in a modal popup, on clicking that button another modal popup opens on top of that. Now I want to refresh the containing page of parent modal dialog on closing child popup.

my code snippet in parent popup :

function OpenModalPopup(_url) {
        var options = {
            url: _url,
            title: "Modal Popup",
            allowMaximize: true,
            showClose: true,
            dialogReturnValueCallback: Function.createDelegate(null, closewindow)
        };
        SP.UI.ModalDialog.showModalDialog(options);
    }

    function closewindow() {
    SP.UI.ModalDialog.RefreshPage(SP.UI.DialogResult.OK);        
    }

But it refreshes the full page