The Page ID of the shared page was replaced by this page.
GMMR0AllocateHandyPages expects this to indicate a shared page that has been replaced by this page and should have its reference counter decremented and perhaps be freed up. Use NIL_GMM_PAGEID if no shared page was involved.
All other APIs expects NIL_GMM_PAGEID here.
All APIs sets this to NIL_GMM_PAGEID.