From owner-freebsd-hackers Thu May 25 13:22:51 2000 Delivered-To: freebsd-hackers@freebsd.org Received: from apollo.backplane.com (apollo.backplane.com [216.240.41.2]) by hub.freebsd.org (Postfix) with ESMTP id 1E40537B6B6 for ; Thu, 25 May 2000 13:22:46 -0700 (PDT) (envelope-from dillon@apollo.backplane.com) Received: (from dillon@localhost) by apollo.backplane.com (8.9.3/8.9.1) id NAA84015; Thu, 25 May 2000 13:22:40 -0700 (PDT) (envelope-from dillon) Date: Thu, 25 May 2000 13:22:40 -0700 (PDT) From: Matthew Dillon Message-Id: <200005252022.NAA84015@apollo.backplane.com> To: Anatoly Vorobey Cc: hackers@FreeBSD.ORG Subject: Re: Proper uses for MFS? References: <200005251705.NAA67491@blackhelicopters.org> <200005251757.KAA83404@apollo.backplane.com> <20000525141623.D6776@sasami.jurai.net> Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG :You, Matthew Dillon, were spotted writing this on Thu, May 25, 2000 at 10:57:33AM -0700: :> :> I don't particularly like to use MFS for 'large' partitions, mainly :> because cached data blocks wind up in core memory twice (once in MFS's :> memory map, and once in the VM page cache). : :You've said this several times in threads on MFS during recent months, :and I've always wanted to ask: is that a necessary 'feature' of MFS's :architecture, or something which could possibly be fixed without :too much hard work? For instance, would it be possible to force :VM not to cache MFS pages, etc.? : :-- :Anatoly Vorobey, The double caching is a consequence of MFS's 'physical media' being the mmap() rather then real physical media. It would be difficult to fix, and probably not worth the effort. MFS's only advantage is that the double-caching tends to keep pages in-core longer, and you have less 'real' physical I/O because things like write-behind and buffer cache flushes are doing nothing more then flusing from the kernel's main VM page cache into MFS's memory map. If you have enough memory not to care about the double-caching issue, then MFS will work fine. -Matt Matthew Dillon To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message