GC logging with "-XX:+UnlockDiagnosticVMOptions -XX:G1SummarizeRSetStatsPeriod=1 -Xlog:gc+remset=trace" would always print zero total refined cards under "Before GC RS summary".

This is because after JDK-8231153, the counters for total refined cards are updated in policy()->record_collection_pause_start(), which is executed after gc_prologue() that executes rem_set()->print_periodic_summary_info().