Our contact from Oculus reported a performance issue on 2017.3 to XR devs and we XR QA are able to repro the issue.
Basically, comparing to 2017.2, when VR is enabled and entering playmode, GPU commited bytes increased about 100MB. We are not sure if this is by design or bugs, need VR gfx devs to investigate.

Repro steps:
1) Create an empty project using 2017.2.1p3.
2) In quality settings, set anti alias to 8x. In XR settings, enable XR support and select Oculus SDK. Make sure OculusRift is hooked up and ready to use.
3) Open Process Explorer (an open source tool) and find Unity processes.
4) Enter playmode, observe GPU memory usage numbers
5) Open the same project in 2017.3.0p4 and do the same, observe the increased GPU memory usage numbers.