Mutator-Driven Object Placement using Load Barriers

Object placement impacts cache utilisation, which is itself critical for performance. Managed languages offer fewer tools than unmanaged languages in the way of controlling object placement due to the abstract view of memory. On the other hand, managed languages often have garbage collectors (CC) that move objects as part of defragmentation. In the context of OpenJDK, Hot -Cold Objects Segregation GC (HCSGC) added locality itnprovement on -top of ZCC by piggybacking on its loaded value -harrier based design. In addition to the open problem of tuning HCSGC, we identify a contradiction in two of its design goals and propose LR, that addresses both these problems. We implement LR on-top of ZCC and compare it with GCs in OpenJDK and with the best performing HCSGC configuration using DaCapo, JCraphT and SPECjbb2015. While using less resources, LR outperforms HCSGC in 18 configurations, matches performance in 17, and regresses in 3.