Subject: Swap overcommit (was Re: Replacement for grep(1) (part 2))
To: Matthew Dillon <>
From: Charles M. Hannum <>
List: tech-userlevel
Date: 07/13/1999 19:46:57
>     And disallowing overcommit also does not give applications the *choice*
>     of dealing gracefully, because they often cannot deal with the
>     situation where they might be refused a reasonable request for memory.

That's objectively false.  The application could do something useful
if it wanted to.  That most applications don't isn't relevant.  The
system can at least provide the mechanism.

>     But back to your 1000-hour simulation:  If you are running it on an
>     environment designed to deal with thousand-hours simulations, then
>     you are obviously going to have sufficient swap such that your 
>     simulation will never get the axe anyway.

That's also objectively false.  Most such environments I've had
experience with are, in fact, multi-user systems.  As you've pointed
out yourself, there is no combination of resource limits and whatnot
that are guaranteed to prevent `crashing' a multi-user system due to
overcommit.  My simulation should not be axed because of a bug in
someone else's program.  (This is also not hypothetical.  There was a
bug in one version of bash that caused it to consume all the memory it
could and then fall over.)

>     It's easy to come up with potentials, but try assigning a probabilty
>     to them and see how much they make sense then.  If you've been running
>     thousand-hour simulations for 20 years and not a single one has ever
>     been blown away due to the system running out of swap, then it obviously
>     isn't an issue.

And lastly, that is also objectively false.  Just because I haven't
been screwed yet (and, in fact, I *have* been), that doesn't mean I
won't be screwed in the future.