Igor Braga, Jonathan Oommen GC optimizations you never knew existed

You re probably familiar with the wellknown Garbage Collection policies such as CMS, G1, Shenandoah, ZGC, gencon, balanced, etc. Many GC optimizations can go unnoticed if not paid close attention. This talk is meant to demystify some of these optimizations that even though might be transparent to a JVM user, makes a tremendous performance impact. We ll start the talk by going over two wellknown OpenJ9 GC policies, balanced and CS gencon as a preparation for the main part of the talk. Once we have the necessary background well dive into Dynamic breadthfirst scan ordering which is a scan ordering algorithm that takes into consideration the hotness of a field. The second optimization we ll share is double mapping of arraylets which is a way to improve memory management of large arrays in regionbased GCs. Finally, we ll share be sharing Offheap technology for regionbased Collectors which is a way to optimize large object allocation for regionbased GCs.