Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uwm.edu!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!dali.cs.montana.edu!milton!uw-beaver!Teknowledge.COM!unix!garth!fouts@bozeman.ingr.com (Martin Fouts) From: fouts@bozeman.ingr.com (Martin Fouts) Newsgroups: comp.arch Subject: Re: Architectural Requirements for Unix (was: upgrades) Message-ID: <446@garth.UUCP> Date: 9 Jun 90 00:39:43 GMT References: <29972@cup.portal.com> <1990May14.141148.9884@xavax.com> <7754@crdgw1.crd.ge.com> <30016@cup.portal.com> <1990May19.230618.16090@utzoo.uucp> <383@garth.UUCP> Sender: fouts@garth.UUCP Organization: INTERGRAPH (APD) -- Palo Alto, CA Lines: 89 In-reply-to: peter@ficc.ferranti.com's message of 31 May 90 18:46:48 GMT In article peter@ficc.ferranti.com (Peter da Silva) writes: In article <383@garth.UUCP> fouts@bozeman.ingr.com (Martin Fouts) writes: > 3) Smaller is "better". If I have to solve a 1000^3 grid, I have to > solve it. I've done it with segmented memory in the small (Y/MP) > and segmented memory in the large (Cray 2) and virtual memory > (ETA/10.) For my purposes, the Cray 2 was best. Your milage would > vary. In turn, you're making a false assumption: that there's something inherent in these very large programs (VLPs) that people are complaining about that requires them to be large. Nobody is denying that some problems require big iron. Text processing, text editing, window systems, and so on... the majority of VLPs that come under fire... have no inherent reason to be very large. Even machines as small as a 128K Mac can run excellent windowing systems, and editors and text processors are even smaller. Say What!? There are *no* assumptions in my comments, which were based on measurements. I said for a particular problem (and hinted at its nature) that a particular machine was *measured* to perform better. I then qualified the statement by noting that it wouldn't hold in all cases: "Your milage would vary." > I need paging. I need it to keep the total amount of memory I am > using small and make my programs more efficient by: > 1) Using implicit sharing of text segments This does not require paging. Look at good old PDP-11 UNIX. Doesn't require, but can use. > 2) Using copy on write sharing of forked images This requires paging. Fork() is a poor match for a non-demand-paged architecture. My reaction is that we don't need fork(). > 3) Using explicit sharing of library code This does not require paging. Look at good old PDP-11 RSX. Doesn't require, but can be much easier to do. It is often harder to manage the usually smaller number of segments than the usually larger number of pages > 4) Using explicit sharing of multithreaded applications This does not require paging. Look at the Transputer. Look at the Cray 2. But it's easier to do if you have them. > 5) Using good locality of reference to minimize resident sets This is the big win for paging systems. You don't need to pull any more reasons out of the hat. However, when you have a small program anyway this becomes much less important. Ture. The question shouldn't be "is paging good" or "is paging bad" or "who needs it". The question is "do you need it". I wasn't dealing with good/bad. I was asked "who needs it?" and I answered me. I'm not sure that the difference between "who needs it" and "do you need it" is worth using two statements for. Also, paging and bloated programs are not synonymous. People can write bloated program with overlays: look at the OS/360 kernel as described in the Mythical Man-Month. The problem isn't paging. The problem is people who think that because memory is cheap they can act like it's free. That is what I was trying to say. I won't be subtle this time: 1) Paging can be abused 2) Paging can be used for many things. 3) Some of these things can be done other ways. 4) Taken as a whole, they make paging worth the effort. Marty -- Martin Fouts UUCP: ...!pyramid!garth!fouts ARPA: apd!fouts@ingr.com PHONE: (415) 852-2310 FAX: (415) 856-9224 MAIL: 2400 Geng Road, Palo Alto, CA, 94303 If you can find an opinion in my posting, please let me know. I don't have opinions, only misconceptions.