Date: Wed, 16 Jan 2008 11:54:40 -0500 From: Bill Moran <wmoran@potentialtech.com> To: Albert.Shih@obspm.fr Cc: Dan Nelson <dnelson@allantgroup.com>, freebsd-questions@freebsd.org Subject: Re: How manu swap ? Message-ID: <20080116115440.6510872c.wmoran@potentialtech.com> In-Reply-To: <20080116163701.GV89314@pcjas.obspm.fr> References: <20080116150454.GP89314@pcjas.obspm.fr> <20080116162805.GH97708@dan.emsphone.com> <20080116163701.GV89314@pcjas.obspm.fr>
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In response to Albert Shih <Albert.Shih@obspm.fr>: > Le 16/01/2008 =E0 10:28:06-0600, Dan Nelson a =E9crit > > In the last episode (Jan 16), Albert Shih said: > > > Hi all > > >=20 > > > I known it's classic question.=20 > > >=20 > > > Long time ago when I install a FreeBSD x86 32 bits when I have N Go > > > of Ram the installer take 2xN Go for the swap partition. > > >=20 > > > Now I just install two machine with FreeBSD amd64 version with 8Go of > > > Ram and FreeBSD installer take 4 Go of swap. > > >=20 > > > Is a bug in the installer or now FreeBSD don't need 2xRam of swap ? > >=20 > > When was the last time you saw your swap partition with more than 2GB > > in use? On an 8GB system, you probably will either never have enough > > processes to require swapping at all, or you will have one or two > > processes so big that if they ever swap, it's a sign you need more RAM, > > not more swap :) In systems with that much RAM, swap is pretty much > > only used for crashdumps, and with minidumps enabled by default, you This is really a pretty narrow view of things. * Swap _can_ be used to extend a systems usability beyond what it was originally designed for. If you don't exceed the physical RAM by too great a margin, allowing a few little-used processes to page out while heavy use processes use all available memory is not a big performance hit. * The idea that an 8G system will never use all that RAM is laughable to me. I can easily create applications that eat up 8G of RAM, legitimately. * In the event that something unexpected happens, having a lot of swap can save your ass by causing the system to slow down instead of kill processe= s. * Disk space is cheap. 16G of swap costs what? 15G of 15,000 RPM SCSI hard drive space costs $40 -- not much for piece of mind. * Of course, the crash dumps that are mentioned. I agree, though, that swap isn't what it used to be. Nobody uses it as supplemental RAM any more as far as I can tell. It's pretty much just a safety net nowadays. --=20 Bill Moran http://www.potentialtech.com
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