[bjourne]

That's a good explanation of why I'm wrong. Basically you are hoping to reach an equilibrium situation in which 0% of the allocated memory in nursery are true survivors. Because if the true survival rate was higher than 0%, then the larger the nursery size the longer the duration between collections and the higher the number of objects that are true survivors.

If you had a perfect situation like that, with a giant nursery, you wouldn't even need to gc anything. When the nursery is full, just start over from address 0 and you can be confident that when the new objects starts overwriting the old that the old will already be unreachable from the object graph.

You never reach that situation in reality. Even in a simple web server some request handling thread might do something innocuous like setting a key in a cache hash somewhere leading to the hash being full and needing to be reallocated. That would dirty mark one card. And again, the longer the duration, the more of these "freak" events you get. Or there may be a string somewhere that keeps track of the current date and when it ticks over from "July 31st, 2015" to "August 1st, 2015" it triggers a reallocation because the last string is one character longer.

It may be that having a large nursery is a good trade-off because for many loads it's the same cards being marked over and over again. That may outweigh the increased frequency of tenured generation collections (memory isn't free so you must take the space from somewhere).