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The large binary GC is actually pretty simple too: Shared binaries are refcounted; the references are in the process heap. When the references are GCed from the process, the shared binary can be freed. The reason that sometimes it takes a long time to free, is that some types of processes will get references to a large number of binaries, but not trigger a process garbage collection, leaving lots of binaries allocated in the shared space. Garbage collection for a process is only automatically triggered when the process heap would grow, so there are some common cases which result in bad behavior: processes that don't generate much garbage on their heap, but do touch a lot of binaries (often this is request routing); processes that grow their heap to some large size doing one kind of work, but then switch to another type that doesn't use much heap space, leaving a long time between GC; processes that touch a lot of binaries but then don't do any processing for a long time (maybe a periodic cleanup task).

Another common issues is taking references to a small part of a large shared binary.