Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!pt.cs.cmu.edu!MATHOM.GANDALF.CS.CMU.EDU!lindsay From: lindsay@MATHOM.GANDALF.CS.CMU.EDU (Donald Lindsay) Newsgroups: comp.arch Subject: Inverted Page Tables Message-ID: <8106@pt.cs.cmu.edu> Date: 21 Feb 90 22:43:56 GMT References: <9708@spool.cs.wisc.edu> <20270@cfctech.cfc.com> <11112@encore.Encore.COM> <753@dgis.dtic.dla.mil> <3606@uceng.UC.EDU> <757@dgis.dtic.dla.mil> <4852@scolex.sco.COM> <29718@brunix.UUCP> <6998@celit.fps.com> <43367@ames.ar Organization: Carnegie-Mellon University, CS/RI Lines: 21 In article <43367@ames.arc.nasa.gov> lamaster@ames.arc.nasa.gov (Hugh LaMaster) writes: >1) Several posters have mentioned that there is some unspecified but obvious >(to them) major problem with using inverted page tables together with >memory mapped files. I wonder if someone could enlighten us regarding >this problem, since apparently it isn't obvious to every system architect :-) The big problem is with sharing. The word "inverted" is used, because the table is a map from physical addresses to virtual addresses. More precisely, you use an array, and use physical page numbers as subscripts. Each table entry tells you what virtual page is mapped to there. SO: only one page can be mapped to there. Unless, of course, the OS goes through a fair bit of grief to make the machine work right in spite of its design. -- Don D.C.Lindsay Carnegie Mellon Computer Science