I just created a text file (Language > None (Normal Text)) with ~16M copies of the line this is just one line, with 1 in 1024 having -- with extra appended to the end.

When I search forward or backward for extra (SearchMode=Normal, not Regular Expression), it takes the same amount of time to search forward or backward. It’s definitely slow – as is everything when dealing with 10M lines – especially for Ctrl+HOME or Ctrl+END, but I don’t notice any difference between forward and backward search.

You might check your Settings > Preferences > Performance settings, and see if any of those help. If your log file is being syntax highlighted, you might want to change the performance threshold so that it’s not syntax highlighted, and it might speed up.

(If you were using Regular Expression search mode, and you had done the power-user config to allow backward regex, you need to know that backwards regex are not as efficient as forward, because the regex engine wasn’t optimized for backwards search.)