Comment # 16 on bug 1166965 from Steve Kowalik

My current testing has shown:

2.3.1:  Maximum:  2455.90MiB
2.4.0:  Maximum:  6736.48MiB
2.4.1:  Maximum:  6622.50MiB
2.4.2:  Maximum:  6635.35MiB
2.4.3:  Maximum:  6706.11MiB
2.4.4:  Maximum:  6548.39MiB
3.0.0*: Maximum:  2505.21MiB

[*]: Released yesterday, requires a patch to conf.py due to cdomain changes,
     and given the whole heap of warnings printed, I'm not confident about the
     quality of the resultant docs anyway.

I think we'll revert Factory to Sphinx 2.3.1 until the kernel supports 3.0.0.