Date: Fri, 23 Feb 2001 21:31:17 -0600 From: Mike Meyer <mwm@mired.org> To: Sven Brandenburg <sven@crashme.org> Cc: questions@freebsd.org Subject: Re: 4.2-STABLE weird behaviour without swap Message-ID: <14999.11013.348462.189477@guru.mired.org> In-Reply-To: <54384197@toto.iv>
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Sven Brandenburg <sven@crashme.org> types: > Is it possible that FreeBSD has some very strange problems > when the system is configured without any swap partitions? Yup. Running out of virtual is bad juju, and probably not very well tested. > 3 weeks ago, i threw another DIMM into that box, having 1G of > memory now. At the same time I decided that this amount of mem > should be sufficient and disabled swap. The main service on this > host eats huge ammount of memory during its operation but for > this application its better to get an "out of memory" and a > following application crash (and restart) than having the > performance penalty of a swapping system. Let's think about this. Until you've used all your real memory, there isn't going to be any difference between having swap and not having swap (unless you've turned on NO_SWAPPING in the kernel, in which case you'll have an extra bit of real because of the code you diked from the kernel). So you do something that runs you out of real memory. In the situation you've got now, your application crashes, and the system may do strange things as well do to being in an unusual state. If you left swapping turned on, some page the system figures it won't need for a long time would get swapped out to make room for the running application. This slows down the current application when it needs RAM - you have to swap something out - and the applications whose pages got swapped out if they ever want those pages again (and it may be the same application, and those pages may never be wanted again). In other words, you've turned a fail-soft situation (things slow down when you run out of real) into a fail-hard situtation (things die when you run out of real), possibly with no performance change before failure. Is that really what you want to do? > Is it generally a stupid idea to have no swap at all? It's like running -current - you *really* need to know what you're doing. <mike -- Mike Meyer <mwm@mired.org> http://www.mired.org/home/mwm/ Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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