Export large data from Gridview and Datareader to an Excel file using C#

protected void btnExportFromDatagrid_Click(object sender, EventArgs e)
{
ExportGridToExcel(grdStudentMarks, "StudentMarks.xls");
}
public void ExportGridToExcel(GridView grdGridView, string fileName)
{
Response.Clear();
Response.AddHeader("content-disposition",
string.Format("attachment;filename={0}.xls", fileName));
Response.Charset = "";
Response.ContentType = "application/vnd.xls";

StringWriter stringWrite = new StringWriter();
HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);
grdGridView.RenderControl(htmlWrite);
Response.Write(stringWrite.ToString());
Response.End();
}


Overiding VerifyRenderingInServerForm Method

public override void VerifyRenderingInServerForm(Control control)
{
  /* Confirms that an HtmlForm control is rendered for the specified ASP.NET
     server control at run time. */

}