Huge memory usage in Nonpaged Pool
Solution 1:
Found it, you can add the column "NP Pool" to the "Processes" tab on Task Manager:
In my case, the culprit was Fling File Transfer, which has a serious memory leak. It was using more than 2 GB of the nonpaged memory pool before I restarted it. The above screenshot shows it after running for two minutes.
Bug report filed.