From owner-freebsd-questions@FreeBSD.ORG Wed Sep 9 16:01:16 2009 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E64101065672 for ; Wed, 9 Sep 2009 16:01:16 +0000 (UTC) (envelope-from jerrymc@gizmo.acns.msu.edu) Received: from gizmo.acns.msu.edu (gizmo.acns.msu.edu [35.8.1.43]) by mx1.freebsd.org (Postfix) with ESMTP id 8DFB38FC1A for ; Wed, 9 Sep 2009 16:01:16 +0000 (UTC) Received: from gizmo.acns.msu.edu (localhost [127.0.0.1]) by gizmo.acns.msu.edu (8.13.6/8.13.6) with ESMTP id n89FuvV2022697 for ; Wed, 9 Sep 2009 11:56:57 -0400 (EDT) (envelope-from jerrymc@gizmo.acns.msu.edu) Received: (from jerrymc@localhost) by gizmo.acns.msu.edu (8.13.6/8.13.6/Submit) id n89Fuv5p022696 for freebsd-questions@freebsd.org; Wed, 9 Sep 2009 11:56:57 -0400 (EDT) (envelope-from jerrymc) Date: Wed, 9 Sep 2009 11:56:57 -0400 From: Jerry McAllister To: "'freebsd-questions@freebsd.org'" Message-ID: <20090909155657.GB22575@gizmo.acns.msu.edu> References: <7B9397B189EB6E46A5EE7B4C8A4BB7CB3037EBB7@MBX03.exg5.exghost.com> <20090908235259.GB19173@gizmo.acns.msu.edu> <20090909105707.GA27941@torus.slightlystrange.org> <20090909145922.GB22253@gizmo.acns.msu.edu> <20090909154655.GA96342@torus.slightlystrange.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090909154655.GA96342@torus.slightlystrange.org> User-Agent: Mutt/1.4.2.2i Subject: Re: Using mdconfig for swap space X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 09 Sep 2009 16:01:17 -0000 On Wed, Sep 09, 2009 at 04:46:56PM +0100, Daniel Bye wrote: > On Wed, Sep 09, 2009 at 10:59:23AM -0400, Jerry McAllister wrote: > > On Wed, Sep 09, 2009 at 11:57:07AM +0100, Daniel Bye wrote: > > > > > On Tue, Sep 08, 2009 at 07:52:59PM -0400, Jerry McAllister wrote: > > > > On Tue, Sep 08, 2009 at 04:51:20PM -0500, Peter Steele wrote: > > > > > > > > > Are there any advantages to using mdconfig and creating a virtual disk for swap space as opposed to having a designated swap partition? For example, I could do something like this: > > > > > > > > Unless I am missing something basic here, it seems like a bad idea to > > > > me - to carve out and use up some memory to use as extra storage for > > > > processes that need more memory that you have taken away to give to swap. > > > > That is self defeating. > > > > > > > > In addition, one use of swap is to write dumps to if there is a crash. > > > > If you put it in memory, it is gone when you reboot. > > > > > > He's talking about using a swap file, rather than a dedicated partition on > > > the disk, not in RAM! Although it is slightly slower, as Chuck has already > > > pointed out, it might, in certain circumstances, be a somewhat more > > > convenient solution than repartitioning/reinstalling the whole system. > > > > > > And as RW has said, the facility already exists and can be enabled with a > > > couple of knobs in /etc/rc.conf. > > > > I understand using a file and making it in to swapspace. I have used that > > a couple of times when I needed to add some swap space temporarily. But > > isn't the command he is trying to use (mdconfig) for creating a memory > > filesystem - eg use a chunk of memory and make a file from it (then use it > > for swap or whatever)? That is in RAM. > > No, with the -t vnode and -f options, he'd actually be creating > a file-backed memory disk. The terminology can be a little confusing, but > in this instance the file wouldn't be loaded into RAM, but would instead > be treated as any other disk-like device. It's exactly the same approach > as used by /etc/rc.d/addswap, which gets its configuration from $swapfile > set in /etc/rc.conf. I see that now, but it seems like the long way around to get to what you get with a swapon. Oh well. ////jerry > > Dan > > -- > Daniel Bye > _ > ASCII ribbon campaign ( ) > - against HTML, vCards and X > - proprietary attachments in e-mail / \