使用FileStream ASPNET发送大文件500MB时出现OutOfMemoryException

public void DownloadFile(string fileName)
{
    const int bufferSize = 1024 * 1024; // 1MB
    using (var fileStream = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite, bufferSize))
    {
        Response.BufferOutput = false;
        Response.ContentType = "application/octet-stream";
        Response.AppendHeader("Content-Disposition", $"attachment; filename={Path.GetFileName(fileName)}");
        var buffer = new byte[bufferSize];
        int bytesRead;
        while ((bytesRead = fileStream.Read(buffer, 0, bufferSize)) > 0)
        {
            Response.BinaryWrite(buffer);
            Response.Flush();
            Array.Clear(buffer, 0, bufferSize);
        }
    }
}

public void DownloadFile(string fileName)
{
    Response.BufferOutput = false;
    Response.ContentType = "application/octet-stream";
    Response.AppendHeader("Content-Disposition", $"attachment; filename={Path.GetFileName(fileName)}");
    Response.TransmitFile(fileName);
}