On Sat, 15 Aug 1998, Albert D. Cahalan wrote:
>
> Matt Agler writes:
>
> > Hmm, doesn't that seem a bit complicated? The whole problem here is that
> > the computer really has no knowledge of what should and should not be
> > killed. You're just making elaborate guesses.
>
> Exactly. It is no worse than deciding what to swap out. Linux has no
> knowledge of what will be needed next, yet it makes decisions about
> what should be swapped or thrown out.
>
> > The kernel can't read the users mind to find out which process
> > is least important. There's no static mapping between size,
> > priority, resource use, etc. to importance.
>
> That is right. So what? The computer can't just wait for an admin.
> It can kill random processes (bad) or kill selected processes (not worse).
> Other options include halt, hard reboot, and crash.
>
> Our current situation is bad. At the very least, Rik van Riel's process
> killer will not be worse than what we already have. I expect that most
> people will find it much better than merely "not worse" though.
>
> > It would be better and simpler to let the user or admin decide what to
> > kill. Instead of killing a process, we should put it to sleep.
>
> End result: 100% memory use, 100% idle, all processes stopped.
>
> > If the machine has overextended itself, we're probably swapping like mad
> > already. It's hammered. We're not getting anything done. We don't need
> > efficiency anymore. We want recovery without loosing in-process work.
>
> Not possible.
>
> > For example, let's put each process, that asks for a page that we can't
> > give, to sleep (from do_no_page?). This would be a special sleep in that
> > it doesn't wakeup until we return to a certain threshold of free memory.
> > What would happen is that it's pages would age and get thrown out.
>
> Thrown out? You must mean that literally, since there may be no more swap.
> The process will be really messed up if you send pages to /dev/null.
>
> > Other processes would complete.
>
> No they wouldn't, since they need memory too. They may also be long-lived
> daemon processes.
>
> > The load would be reduced until the machine was recoverable.
> >
> > root could login and fix the problem, add swap, kill stuff, whatever.
> ...
> > Admittedly, root would need to allocate memory and so any root processes
> > should probably be exempt.
>
> Hostile users can just use a daemon to grab the last bit of memory
> that you reserved for root. (finger, telnet, whatever)
>
> With the overcommit, random events could be enough to eat up all
> the reserved space.
>
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