> mmap.mmap(-1, 2**31 + 5) could be used here.

Yeah, I hesitated to use mmap, but I'm not really a big fan of using directly a mmap object in test_descr. Unit tests are supposed to only test one thing.


> If the pages are never touched it won't increase the working set size. It merely maps the address range with demand-zero pages.

It depends on the Kernel configuration. On Solaris, overcommit is disable by default.

I prefer to use a regular Python str. Or maybe use a custom Python object for which we can control the output of __len__()?