Date: Wed, 3 May 2000 09:32:50 +1000 From: Phil Homewood <pdh@bit.net.au> To: freebsd-questions@FreeBSD.ORG Subject: Re: BSD Theology: swap, /var, /tmp and /usr/tmp Message-ID: <20000503093249.A22805@atlas.bit.net.au> In-Reply-To: <20000503012329.A3265@student.csd.uu.se>; from ertr1013@student.csd.uu.se on Wed, May 03, 2000 at 01:23:29AM %2B0200 References: <390F41FD.5880279E@telinco.net> <20000503012329.A3265@student.csd.uu.se>
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Erik Trulsson wrote: > The idea behind the 2*memory rule is basically that if you need to use more > memory than twice your physical memory the system will have such lousy > performance due to all the swapping that you really want more RAM. My understanding was as follows: * Suppose you have N Mb of RAM. Assume that N is relatively large such that kernel footprint and minimal necessary processes occupy negligible fraction of N. * Suppose you have a process P which needs to use around N Mb of RAM. Suppose that all RAM is in use. (ie, worst case for swapping.) If you have less than 2*N swap, you do not have enough room to swap out everything else in the N Mb of RAM to swap in (and out) the N Mb image required by process P in one hit, so you need to do it in smaller chunks, which thrashes the disk. If you have > 2*N Mb of swap (plus any required for other swapped out processes) then you can swap the image of P in and out with minimal overhead. Is this correct? To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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