GoFree: Reducing Garbage Collection via Compiler-Inserted Freeing

Abstract

In a memory-managed programming language, programmers allocate memory by creating new objects, but programmers never free memory. A garbage collector (GC) periodically reclaims memory used by unreachable objects. As an optimization based on escape analysis, some memory can be freed explicitly by instructions inserted by the compiler. This optimization reduces the cost of garbage collection, without changing the programming model. We designed and implemented this explicit freeing optimization for the Go language. We devised a new escape analysis that is both powerful and fast (𝑂(𝑁^2) time). Our escape analysis identifies short-lived heap objects that can be safely explicitly deallocated. We also implemented a freeing primitive that is safe for use in concurrent environments. We evaluated our system, GoFree, on 6 open-source Go programs. GoFree did not observably slow down compilation. At run time, GoFree deallocated on average 14% of allocated heap memory. It reduced GC frequency by 7%, GC time by 13%, wall-clock time by 2%, and heap size by 4%. We open-source GoFree.