From owner-freebsd-hackers Sat Jul 17 18:48:30 1999 Delivered-To: freebsd-hackers@freebsd.org Received: from apollo.backplane.com (apollo.backplane.com [209.157.86.2]) by hub.freebsd.org (Postfix) with ESMTP id 5E1AF14D06 for ; Sat, 17 Jul 1999 18:48:26 -0700 (PDT) (envelope-from dillon@apollo.backplane.com) Received: (from dillon@localhost) by apollo.backplane.com (8.9.3/8.9.1) id SAA88154; Sat, 17 Jul 1999 18:48:18 -0700 (PDT) (envelope-from dillon) Date: Sat, 17 Jul 1999 18:48:18 -0700 (PDT) From: Matthew Dillon Message-Id: <199907180148.SAA88154@apollo.backplane.com> To: David Miller Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: 650 MB MFS? References: Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG : :I'm not sure what good that will do me. The point of the exercise is to :ensure that cdrecord never has to wait on enough seeks to create coasters. :Putting it all in ram before starting should do this, but a different :interface to the same data on disk doesn't. : :Unless I'm missing something, which is usually the case:) : :Thanks for the answers Matt! : :--- David MFS isn't very efficient - when you read the data it will be stored in memory twice. This is because MFS's 'disk' is a process's VM space, which happens to be memory which is *different* memory then the VM cache. So each page is stored in memory twice. If you have enough ram... say you have 1GB of ram, and you create a normal image file on disk, the system will be able to hold the entire contents of the file in the VM cache as a matter of course. This would be fairly easy to test. Create the image file, then do a read pass on it: dd if=imagefile of=/dev/null bs=32k Then do another read pass on it while running 'iostat 1'. xterm1> iostat 1 xterm2> dd if=imagefile of=/dev/null bs=32k If you don't get significant disk activity then the entire file has been cached in ram and you should be able to cdrecord it. You can test both mechanisms by running 'iostat 1' while trying each one. Then use whichever one is better. If you don't have a gig of ram, MFS isn't going to help you since the pages will be forced out to swap and cause disk I/O to occur when they are brought back in. -Matt Matthew Dillon To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message