Subject: Re: Swap overcommit (was Re: Replacement for grep(1) (part 2))
To: Daniel C. Sobral <>
From: Tim Vanderhoek <>
List: tech-userlevel
Date: 07/15/1999 01:56:19
On Thu, Jul 15, 1999 at 01:48:40PM +0900, Daniel C. Sobral wrote:
> > 
> > If you have a lot of users, all of which have buggy programs which eat
> > a lot of memory, per-user swap quotas don't necessarily save your butt.
> The chance of these buggy programs running at the same time is not
> exactly high...

Well, it is higher than your probably giving credit for.  Suppose
Professor A. hands-out X assignment.  Unfortunately, some piece of
code he supplied to his, let's say 200 students ignorant first year
students, has this particular memory-eating bug.  Being ignorant
first-year students, they will notice something is wrong, assume
the problem is their fault, and repeat the exact same procedure
five or so times.  Again, being ignorant first year students, they
will probably all be using the same shell server.

To make things worse, some wise-ass may have told a bunch of them how
to use ulimit or limit in order to push their available resources as
high as possible (perhaps very high, since the admin hopefully
recognizes that sometimes students need high resource limits to
perform research).

Fortunately, overcommit rescues the machine and kills those buggy
programs instead of letting them spin around for ever in some kind of
"malloc() failed ... must be temporary failure, wait and retry".

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