Date: Thu, 11 Dec 2003 00:26:20 -0000 From: "Sparrevohn, Thomas" <thomas.sparrevohn@eds.com> To: bv@wjv.com, freebsd-isp@freebds.org Cc: freebsd-hackers@freebsd.org Subject: RE: adding more ram Message-ID: <2946E9F05C8DD511A7DC0002A5608CE401143D3F@gbchm201.exgb01.exch.eds.com>
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The same was true for 10.20 and 11 Versions of HPUX - I believe there once was I very long going debate when the "new" FreeBSD vm was made on the issue. The fundamental question at the time was what to do when you run out of swap/vm space. The 1-1 backing of swap space was seen as a way to avoid that you have resort to kill random processes in order to free up space and the tradition with the 2-1 swap ratio used to have "a performance reason" in the initial Unix Swap and paging implementations. I can't seem to recall the actual reason -----Original Message----- From: owner-freebsd-hackers@freebsd.org [mailto:owner-freebsd-hackers@freebsd.org] On Behalf Of Bill Vermillion Sent: 10 December 2003 14:41 To: freebsd-isp@freebds.org Cc: nbari@unixmexico.com; freebsd-isp@freebsd.org; freebsd-hackers@freebsd.org Subject: Re: adding more ram While normally not able to pour water out of a boot with instructions on the heel, on Wed, Dec 10, 2003 at 02:41 our dear friend Mike Silbersack uttered this load of codswallop: Just one slight addendum here. > I'm replying because I want to answer your real question. > <g> The notion of swap = 2 x ram is an old one, and is no longer > applicable. (Some) older VM systems used very simplistic swapping > mechanisms, which required entire processes to be swapped, thereby > requiring large amounts of swap space. FreeBSD (and other modern OSes) > page out to the swap file in increments of 4K pages, and do so in a > flexible manner. As a result, you should always have *some* swap space > to handle overload cases, but it's not necessary to keep any specific > ram to swap ratio. Systems such as the Irix I used before moving the servers to FBSD around 1996 - reserverd swap space for applications when the application started up so those needed large swap space. Often it was never used, but the design allocated it anyway. Bill -- Bill Vermillion - bv @ wjv . com _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.org"
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