I was curious about these changes to Lua 5.4, so I had a look. When you create a Lua coroutine that allocates 200 Lua stack frames and then yields across them,

I was curious about these changes to Lua 5.4, so I had a look. When you create a Lua coroutine that allocates 200 Lua stack frames and then yields across them, the first longjmp crosses 200ish C stack frames. When you later resume, all those C stack frames are gone, but there wasn't any important state in them! Lua just calls luaV_execute in a loop[0]. (Trampolining?) So at that point, for that coroutine, the lower 200ish Lua stack frames do not have corresponding C stack frames, but any Lua subroutines you then call will have corresponding C stack frames. [0] https://github.com/lua/lua/blob/9b7987a9d1471ba94764286b28e0998f73deb46a/ldo.c#L569 https://github.com/lua/lua/blob/9b7987a9d1471ba94764286b28e0...