Note that the min_free parameter of all stacks is enlarged to 8 K cells if debugging is switched off in order to avoid excessive GC. GC complicates tracing because it renames the _G<NNN> variables and replaces unreachable variables with the atom <garbage_collected>. Calling nodebug/0 does not reset the initial free-margin because several parts of the top level and debugger disable debugging of system code regions. See also set_prolog_stack/2.