From owner-freebsd-fs@FreeBSD.ORG Mon Jan 10 14:03:12 2005 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 8336716A4CE; Mon, 10 Jan 2005 14:03:12 +0000 (GMT) Received: from critter.freebsd.dk (f170.freebsd.dk [212.242.86.170]) by mx1.FreeBSD.org (Postfix) with ESMTP id CBA9243D2F; Mon, 10 Jan 2005 14:03:11 +0000 (GMT) (envelope-from phk@critter.freebsd.dk) Received: from critter.freebsd.dk (localhost [127.0.0.1]) by critter.freebsd.dk (8.13.1/8.13.1) with ESMTP id j0AE3AKJ045045; Mon, 10 Jan 2005 15:03:10 +0100 (CET) (envelope-from phk@critter.freebsd.dk) To: Kris Kennaway From: "Poul-Henning Kamp" In-Reply-To: Your message of "Mon, 10 Jan 2005 05:57:47 PST." <20050110135747.GA44905@xor.obsecurity.org> Date: Mon, 10 Jan 2005 15:03:10 +0100 Message-ID: <45044.1105365790@critter.freebsd.dk> Sender: phk@critter.freebsd.dk cc: FreeBsd-MailGrp cc: Scott Long Subject: Re: using mfs of size > 64Mb and system stability X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 10 Jan 2005 14:03:12 -0000 In message <20050110135747.GA44905@xor.obsecurity.org>, Kris Kennaway writes: > >--HlL+5n6rz5pIUxbD >Content-Type: text/plain; charset=us-ascii >Content-Disposition: inline >Content-Transfer-Encoding: quoted-printable > >On Mon, Jan 10, 2005 at 11:11:44AM +0100, Poul-Henning Kamp wrote: >> In message <20050110100840.29845.qmail@web30301.mail.mud.yahoo.com>, Bara= >th S w >> rites: >> >Initially, I didn't go for swap based fs as I felt >> >that the memory occupied will be from the swap area. >> >As you are saying that the allocation will be from >> >buffer/cache, I will test swap-mfs. >>=20 >> malloc backing should not be used for large disks. >>=20 >> If you _truly_ want to have a large disk which is memory backed, >> you should consider using the "preload" backing as this will withdraw >> the memory entirely from the kernels use. >>=20 >> In general, the benefit from using RAM disks is much smaller than >> most people realize. > >I've found that using a swap-backed disk substantially cuts back on >disk accesses for my purposes [...] Swap-backing is very different from RAM disks in that things get pushed out of RAM if better use can be made of the pages. With RAM disks (preload or malloc backing) you occupy valuable RAM pages with free diskblocks. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.