How can I make pairs.txt?

I basically follow the step which described in this link
https://github.com/umairanis03/facial-recognition/blob/master/validation_prep.md

when i run
python generate_pairs.py --image_dir data --pairs_file_name pairs.txt --num_folds 2 --num_matches_mismatches 3

it never ends.. i waited 3 hours and it was still working without any message.

But if i change the parameter num_matches_mismatches 0, it made a txt file.

what does "num_matches_mismatches" mean? and how can i make pairs.txt file?