7dd0ea74 seems to have tipped this one over,
although 7dd0ea74 itself had only a minimal impact on my local system.

Locally, I measured right before 7dd0ea74:

  Expected    T5631(normal) bytes allocated: 776121120 +/-5%
  Actual      T5631(normal) bytes allocated: 811973144
  Deviation   T5631(normal) bytes allocated:       4.6 %

and at 7dd0ea74:

  Expected    T5631(normal) bytes allocated: 776121120 +/-5%
  Actual      T5631(normal) bytes allocated: 812288344
  Deviation   T5631(normal) bytes allocated:       4.7 %

Reviewed By: austin

Differential Revision: https://phabricator.haskell.org/D936