Tracing garbage collectors have to have some metric for when to trigger a stop-the-world collection. IIRC, many GCs track heap usage and trigger stop-the-world

Tracing garbage collectors have to have some metric for when to trigger a stop-the-world collection. IIRC, many GCs track heap usage and trigger stop-the-world when it gets above a threshold. GC'd language runtimes which don't have a tracing/compacting collector (e.g. CPython with refcounting) don't need to configure a heap size because the behavior doesn't vary as you use up your heap.