title: When does gen 0, gen 1, gen 2 trigger exactly?
body: <p>Gen 0:
  So I read that gen 0 triggers when gen 0 exceeds a size threshold. But I also read that GC is not performed at a "new", because "new" merely slides an address forward. Then, when does it check it has exceeded the threshold to trigger the gen 0 GC?</p>
  
  <p>Gen 1/2:
  Do gen 1/2 have their own size threshold that trigger GC? When do they consider the threshold? Is it the moment when survivors are promoted to the gen? </p>
  
  <p>Does that mean for a gen 1 GC to occur it first checks gen 0, then promotes them to gen 1, only to find gen 1 has exceeded the threshold and so it check gen 1, and check gen 0 again? </p>
  
  <p>And does that mean for a gen 2 GC to occur it first checks gen 0, then promotes them to gen 1, only to find gen 1 has exceeded the threshold and so it checks gen 1, and check gen 0 again. Then promotes gen 0 to gen 1 and gen 1 to gen 2, only to find gen 2 has exceeded the threshold and so it checks gen 2, gen 1 again, and gen 0 again again?</p>