Fix slow unpickling (#21542)
Summary:
This was looking at the number of elements in the memo table, not the total capacity, and was thus calling reserve() a lot more than it should have
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21542
Reviewed By: driazati
Differential Revision: D15723132
Pulled By: jamesr66a
fbshipit-source-id: 20e1f9099b6a51a33994ea9dbc3f22eb3bc0c8f9
