I cannot quite see why the problem is serious: even though the memory is
not returned to the system, it will be swapped out to the swap file, so
it doesn't consume any real memory (just swap space).

I don't think Python should integrate a separate malloc implementation.
Instead, Python's own memory allocate (obmalloc) should be changed to
directly use the virtual memory interfaces of the operating system (i.e.
mmap), bypassing the malloc of the C library.

So I'm -1 on this patch.