[reichstein]

GC is usually not specified to happen at particular times, or saying which values are definitely going to be GCed. Instead it relies on the language semantics, so that any value which is used later in the program, is not going to be GCed. How and when the runtime system determines that a value is not going to be used again is an optimization problem, not a correctness problem.

So everything you quote Lua a saying here is consistent. The thing is that it only considers "used later" as "used later by the Lua program". Or rather, it only considers Lua values as "values". A value stored in non-managed memory is not a value. It's not GCed. The `ffi.new`-created Lua value is, and it's finalizer happens to free the native memory that the pointer refers to.

So non -Lua "values" are not GCed, they are freed as side effects of Lua values being GCed.