only if the full scan of the backmap is performed in excess of a predetermined number of times in a predetermined period for example the heuristic is run only if the full scan of the backmap is performed 3 or more times during 60 seconds this is to make sure that the candidate page is consistently being a burden to the memory management module 350 in still another embodiment the number of times the heuristic of fig5 can be run is limited to once per 1 100 second in one embodiment the heuristic of fig5 keeps track of one candidate page at a time however in other embodiments multiple candidate pages can be kept track of at a time also although in the embodiment of fig5 the heuristic is run to identify the immutable guest physical page it is also possible especially in a para virtualized system to identify the immutable guest physical page by the guest os 220 simply indicating to the memory management module 350 which guest physical page is an immutable guest physical page referring back to fig4 once the immutable guest physical page is identified 504 the memory management module 350 discards 506 existing reverse mappings corresponding to the identified immutable guest physical page additionally the memory management module 350 marks that guest physical page so that it stops 508 adding reverse mappings for that guest physical page this will prevent the memory management module 350 from giving the identified guest physical page back to the guest os 220 to relieve memory pressure it is.