"I can understand the aversion to the waste when its never used - I can address 37851 if you like - it seems pretty simple to fix. The pedant in me must point out that it's 8M of address space, not memory. The cost on 64-bit (well, with a 47-bit user address space) is vanishingly small, ..."

Well, many users pay attention to the RSS value and don't care if the memory is physically allocated or not.

Moreover, I'm not sure that we can fix bpo-37851 in Python 3.7. In general, the policy is to minimize changes in stable Python versions. I'm not sure for Python 3.8 neither. I would suggest to only modify Python 3.9, simply to reduce the risk of regressions.