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SubjectRe: A true story of a crash.
On Sat, 15 Aug 1998, Matt Agler wrote:
> On Sat, 15 Aug 1998, Albert D. Cahalan wrote:
> > 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.
>
> That depends on implementation. Of course, if you let every last page get
> used before doing anything, you're stuck.

Am I missing the point? I was under the impression that there is a
well-defined behavior when a Un*x reaches memory resource limits.
Additional requests for resources are simply denied: currently
executing processes don't get axed until they segfault, get signalled
or exit().

How does the population in user space grow? Only a handful of ways
I can think of:
- malloc(3), realloc, etc.
- fork(2)
- execve(2)
- ...

Each one will fail if there is insufficient virtual memory, so each
application is responsible for detecting NULL from malloc(), -1 from
fork(), and so on, giving it a chance to do other work or exit().

Is this First-Come, First-Served mechanism failing in the case of the
original poster? I suspect that once a few apps exit() from this kind
of starvation, there would still be enough room to run bash and do
sysadmin tasks.

BTW, when you really must have your server under a lighter load to
work properly, there are some obvious adjustments we could make,
including more RAM. Having an emergency swap file/partition would
be nice. On my production (2.0.xx) servers, I have hardware watchdogs
that reset the machine if a certain userland process stops responding
after a few minutes.

_____________________________ Stephen M. Benoit _______________________________
~ ~ | benoits@servicepro.com | B.Eng (Computer), M.Eng (Electrical)
('>') | Tel: +1 514 255-3550 | Service Providers of America INC
_ | FAX: +1 514 256-1356 | Web page: http://www.servicepro.com/
_______|________________________|______________________________________________


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