From owner-freebsd-hackers Wed Jul 14 22:57:15 1999 Delivered-To: freebsd-hackers@freebsd.org Received: from smtp11.bellglobal.com (smtp11.bellglobal.com [204.101.251.53]) by hub.freebsd.org (Postfix) with ESMTP id 4F785150F4 for ; Wed, 14 Jul 1999 22:57:12 -0700 (PDT) (envelope-from hoek@FreeBSD.org) Received: from localhost.nowhere (ppp18406.on.bellglobal.com [206.172.130.86]) by smtp11.bellglobal.com (8.8.5/8.8.5) with ESMTP id BAA07564; Thu, 15 Jul 1999 01:58:56 -0400 (EDT) Received: (from tim@localhost) by localhost.nowhere (8.9.3/8.9.1) id BAA98113; Thu, 15 Jul 1999 01:56:20 -0400 (EDT) (envelope-from tim) Date: Thu, 15 Jul 1999 01:56:19 -0400 From: Tim Vanderhoek To: "Daniel C. Sobral" Cc: Jason Thorpe , tech-userlevel@netbsd.org, freebsd-hackers@FreeBSD.org Subject: Re: Swap overcommit (was Re: Replacement for grep(1) (part 2)) Message-ID: <19990715015619.A97920@mad> References: <199907142127.OAA01681@lestat.nas.nasa.gov> <378D6828.FCC3C120@newsguy.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 0.95i In-Reply-To: <378D6828.FCC3C120@newsguy.com>; from Daniel C. Sobral on Thu, Jul 15, 1999 at 01:48:40PM +0900 Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG 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". -- This is my .signature which gets appended to the end of my messages. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message