When dealing with interpreters, object size size is either implicitly known (for example, basic representation of object has fixed size, like 8 or 32 bytes), or size is stored explicitly on interpreter's level (for example, array size needs to be stored in object header anyway). This means that it may be possible to optimize low-level memory allocation system by not storing memory chunk size (thus saving memory), instead relying that higher levels will pass size explicitly.

Quick look at current sources doesn't show that MicroPython is ideally suited for such optimization, but that's why I write - to propose to add that as a (non-immediate) design goal.

First steps towards that can be simple: make m_free() have signature m_free(ptr, size), and m_realloc(ptr, old_size, new_size), then while going over code to adjust call sites, see if what to pass as "size" param is obvious. In case it's not, well, pass 0, and leave larger refactors to someone who really will implement alternative allocators. Ultimately, there're good reasons for having explicit size field for all variable-length objects, IMHO.