The behavior in this situation is also really bad: it takes a long time for the thread to properly OOM, and sometimes it doesn't! It just trucks along for a very long time (we've confirmed the target doesn't actually take that long to compile in otherwise identical circumstances) and sometimes actually makes it out, or sometimes OOMs. It seems like there's just barely enough headroom for GC to keep scraping memory for a long time--but it's very counterintuitive, because profiling doesn't show us spending much time at all in GC in those situations. Might be some sort of weird thrashing behavior not blocking on GC, hard to say.