With JDK-8340827 only code root sets need to be revised - remembered set cards are estimated using young card estimators (the young gen remset is maintained on the card table and we do not know much about it often).

See if the code root sets actually have an impact, and remove if not really - they add some code after all.

Conversely, maybe try out sampling of the card table to get better estimates about the number of cards into the collection set?