gore@eecs.nwu.edu (Jacob Gore) (10/18/88)
Does Mach (on a NeXT, at any rate) do memory swapping to disk?
If so, what does it use for the swap area at times when the laser disk is out?
(Or are you guaranteed that no page faults or process swapping will occur
while you've got nothing in that drive???)
Jacob Gore Gore@EECS.NWU.Edu
Northwestern Univ., EECS Dept. {oddjob,gargoyle,att}!nucsrl!gorebzs@xenna (Barry Shein) (10/20/88)
>Does Mach (on a NeXT, at any rate) do memory swapping to disk? >If so, what does it use for the swap area at times when the laser disk is out? >(Or are you guaranteed that no page faults or process swapping will occur >while you've got nothing in that drive???) > >Jacob Gore Gore@EECS.NWU.Edu I'll stick my neck out and say that I don't believe that you'll be able to remove the optical disk if that's what you're paging and swapping to (if you have a winch then it's a whole different matter.) I would guess you'd have to bring the system down to a halt to change disks. Even if it could stop everything (eg. treat it like Sun does a netdisk when a server goes down) what could it do when you pop in a different disk? It can't start paging/swapping again, the data on this new disk is all wrong, so you'd be hung anyhow, better to reboot. Reminiscent of Macs with floppies only where you keep a system folder on every application's floppy, only I doubt that's the idea here either. It would be interesting to hear what, if anything, NeXT has done in regards to this. My guess is nothing (ie. to change optical disks you bring the system down, change, reboot, unless you have a winch to run the system off of, or possibly some sort of NFS protocol to direct all swapping/paging to a server.) -Barry Shein, ||Encore||
jsloan@wright.UUCP (John Sloan) (10/20/88)
From article <3924@encore.UUCP>, by bzs@xenna (Barry Shein): : >>Does Mach (on a NeXT, at any rate) do memory swapping to disk? : > It would be interesting to hear what, if anything, NeXT has done in > regards to this. My guess is nothing (ie. to change optical disks you > bring the system down, change, reboot, unless you have a winch to run : I'm sure I've read a quote from Jobs _somewhere_ saying that he thought it was unfortunate that they couldn't figure out a way to change optical disks on the primary drive without rebooting the machine, but that was just the price you had to pay for demand paging. I think it may have been in the Byte BIX article posted to the net by several people. John Sloan +1 513 259 1384 ...!ucsd!ncr-sd!ncrlnk!ncrpcd!wright!jsloan Wright State University Research Center jsloan%wright.edu@csnet-relay 3171 Research Blvd., Kettering, OH 45420 ...!osu-cis!wright!jsloan Logical Disclaimer: belong(opinions,jsloan). belong(opinions,_):-!,fail.
shap@polya.Stanford.EDU (Jonathan S. Shapiro) (10/21/88)
In article <3924@encore.UUCP> bzs@xenna (Barry Shein) writes: >I'll stick my neck out and say that I don't believe that you'll be >able to remove the optical disk if that's what you're paging and >swapping to (if you have a winch then it's a whole different matter.) I don't know that they have done it, but it would be easy enough to have a standalone duplication/file copy program that worked between cd's. Jon
jeff@drexel.UUCP (Jeff White) (10/21/88)
In article <3924@encore.UUCP>, bzs@xenna (Barry Shein) writes: > >Does Mach (on a NeXT, at any rate) do memory swapping to disk? > >If so, what does it use for the swap area at times when the laser disk is out? > >(Or are you guaranteed that no page faults or process swapping will occur > >while you've got nothing in that drive???) > > > >Jacob Gore Gore@EECS.NWU.Edu > > I'll stick my neck out and say that I don't believe that you'll be > able to remove the optical disk if that's what you're paging and > swapping to (if you have a winch then it's a whole different matter.) > > I would guess you'd have to bring the system down to a halt to change > disks. Even if it could stop everything (eg. treat it like Sun does a > netdisk when a server goes down) what could it do when you pop in a > different disk? It can't start paging/swapping again, the data on this > new disk is all wrong, so you'd be hung anyhow, better to reboot. > > Reminiscent of Macs with floppies only where you keep a system folder > on every application's floppy, only I doubt that's the idea here > either. > > It would be interesting to hear what, if anything, NeXT has done in > regards to this. My guess is nothing (ie. to change optical disks you > bring the system down, change, reboot, unless you have a winch to run > the system off of, or possibly some sort of NFS protocol to direct all > swapping/paging to a server.) > > -Barry Shein, ||Encore|| Would it be possible to just turn off the paging/swapping feature? It would seem to me that if you have 8 Mbytes of ram in the machine, you should be able to set up the operating systems to load a program entirely into ram, and then tell the OS that you have no swap space available. (What happens on a standard 4.2/4.3/Mach system now if you have, say, 8-12 Mbytes of ram, but only allocate 2 Mbytes or so of swap space to it?). Unix/Mach is pretty big, but not that big that you couldn't fit it, along with the one or two programs you needed when switching optical disks, into 8 Mbytes of ram. I would think that you should be able to create a program called 'switch', which would turn off most of the unnecessary daemons (cron, accounting, tcp connections), copy the kernal completely into ram, and also copy a small set of programs (stuff like 'ls' or cp', but probably more advanced) which you would need when swapping of copying the optical disks. Jeff White Drexel University - ECE Dept. rutgers!bpa!drexel!jeff
shap@polya.Stanford.EDU (Jonathan S. Shapiro) (10/24/88)
In article <783@drexel.UUCP> jeff@drexel.UUCP (Jeff White) writes: [ The context is a discussion of switching removable optifloppies] > Would it be possible to just turn off the paging/swapping feature? We need to distinguish two sorts of things here. The first is using information actively from two different floppies using 1 drive. The second is copying data between drives. If you will, the issue is interactive versus archival use of the second optifloppy. If the system pages to one device, it is reasonable to expect that even if you *could* address the problem, you wouldn't want to. The need to swap optifloppies would arise too often, and figuring out just what in the UNIX system to make memory resident to manage the problem is nontrivial. If, on the other hand, you are concerned with copying distributed software onto/off-of your active optifloppy, or backing it up, you have something of a different problem, and one which is more practically doable. Mind you, I don't know if NeXT has done this, but here is how I think it might be done: 1. *Swap* out all of the currently running processes. This would use the same mechanism that the BSD kernel uses when paging gets to be too bad. At some point it gives up and forces someone out to make paging work again. 2. flush the buffer cache(s) 3. Swap in whatever system programs you *really* need. 4. Swap in the disk copy program, and make it runnable. 5. Disk copy program can now allocate memory, using a priori knowledge ofthe amount of memory available given the system memory configuration. 6. Disk copy program then copies whatever. 7. Disk copy program exits. OS swaps rest of world back in. Now there are lots of details to worry about, but this strategy might work.