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Path: euryale.cc.adfa.oz.au!newshost.carno.net.au!harbinger.cc.monash.edu.au!munnari.OZ.AU!news.ecn.uoknor.edu!feed1.news.erols.com!howland.erols.net!news.sprintlink.net!news-peer.sprintlink.net!news.sprintlink.net!news-hub.sprintlink.net!news.sprintlink.net!news-fw-6.sprintlink.net!coopnews.coop.net!super.zippo.com!zdc!szdc!szdc-e!news From: "John S. Dyson" <dyson@freebsd.org> Newsgroups: comp.unix.bsd.freebsd.misc Subject: Re: memory allocation problem Date: Sun, 08 Dec 1996 15:19:56 -0500 Organization: John S. Dyson's home machine Lines: 24 Message-ID: <32AB22EC.167EB0E7@freebsd.org> References: <58e60m$pg8@nerd.apk.net> <58f2bn$br2@dismay.ucs.indiana.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Mailer: Mozilla 3.01 (X11; I; FreeBSD 3.0-CURRENT i386) John Fieber wrote: > > In article <58e60m$pg8@nerd.apk.net>, > droberts@apk.net (Dan Roberts) writes: > > Why is everything being allocated to cache?? It works fine as if it were > > actually free. Seems to reallocate well, but why does it do it in the > > first place? > > Because "free" memory is wasted resource. FreeBSD tries to make the > best use of all available memory. When it isn't needed for active > processes, it gets used for other things like cache. > Following up, the memory in the cache queue is immediately available for reuse. There is no reclaimation process needed to use the pages. There are kind-of two kinds of caches on FreeBSD, but they are coherent (exactly the same data, just with a different view.) The page cache is a VM cache, while the VFS (block-buffer) cache is the commonly known buffer cache. The VM cache backs the block buffer cache. The parameter "NBUF(S)" as used in older U**X type kernels is less meaningful on FreeBSD, because a buffer header is not needed for read caching on files. The VM system can provide the cache transparently. John