I tried this as well and the process works normally until it hits the large porn blocklist.
At that point, the size of the swap file slowly grows until it reaches about 750MB out of 1080MB max size.
As this is happening, the tmp files are fairly small compared to the memory consumed:
pi@pi0-2:~$ sudo du -h /tmp/tmp.*
49M /tmp/tmp.4voOUeZw8z.phgpb
8.6M /tmp/tmp.ZM3X0vs3kk.gravity
I stopped the process after about 15 minutes.
This is the blocklist it choked on: https://raw.githubusercontent.com/chadmayfield/my-pihole-blocklists/master/lists/pi_blocklist_porn_all.list