巨大なテキスト ファイルの最後の 10 行を効率的に取得するにはどうすればよいですか?

public static string ReadEndLines(string path, Int64 numberOfLines, Encoding encoding, string lineSeparator) {

    int sizeOfChar = encoding.GetByteCount("\n");
    byte[] buffer = encoding.GetBytes(lineSeparator);


    using (FileStream fs = new FileStream(path, FileMode.Open)) {
        Int64 lineCount = 0;
        Int64 endPosition = fs.Length / sizeOfChar;

        for (Int64 position = sizeOfChar; position < endPosition; position += sizeOfChar) {
            fs.Seek(-position, SeekOrigin.End);
            fs.Read(buffer, 0, buffer.Length);

            if (encoding.GetString(buffer) == lineSeparator) {
                lineCount++;
                if (lineCount == numberOfLines) {
                    byte[] returnBuffer = new byte[fs.Length - fs.Position];
                    fs.Read(returnBuffer, 0, returnBuffer.Length);
                    return encoding.GetString(returnBuffer);
                }
            }
        }

        // handle case where number of lines in file is less than numberOfLines
        fs.Seek(0, SeekOrigin.Begin);
        buffer = new byte[fs.Length];
        fs.Read(buffer, 0, buffer.Length);
        return encoding.GetString(buffer);
    }
}