[benjiweber]

Not an expert but my experience/basic understanding

The old generation gets at lot more expensive as it gets bigger, and I think requires at least some stop the world with all the collectors in hotspot.

New generation collections often remain quick as the size grows as long as most objects are dying young. Increasing the size of new also gives more opportunity for objects to die before being promoted (if you have lots of objects that live just long enough to be promoted it can be a good strategy to increase size of new). New can be collected concurrently.