How does this MOSFET with the configuration of its gate work?
The FET is part of a synchronous buck converter.  The gate driver is also used to drive 2 charge pumps.  

For example, PC170 is charged to 5V minus a diode drop when the FET gate goes low, then pumps that charge onto PC169 when the gate goes high.

This creates a roughly 10V supply for use elsewhere.

The FET gates are drawn differently from the usual convention where the right angle is on the source side, but they are N-FETs.