[Tim]
... Now under 3.7.3. First when phase 10 is done building:
phase 10 adding 9953410 phase 10 has 16743920 objects
# arenas allocated total = 14,485 # arenas reclaimed = 2,020 # arenas highwater mark = 12,465 # arenas allocated current = 12,465 12465 arenas * 262144 bytes/arena = 3,267,624,960
# bytes in allocated blocks = 3,216,219,656
Space utilization is again excellent. A significant number of arenas were reclaimed - but usefully?
Nope! Digging through all the output, all the arena recycling happened in the "_add_ millions of objects" stages, never in the "delete millions of objects" stages. So it was just more accidental arena thrashing (which was recently repaired in bpo-37257).