From owner-freebsd-hackers@FreeBSD.ORG Fri Jan 8 17:38:24 2010 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 1308C106568D for ; Fri, 8 Jan 2010 17:38:24 +0000 (UTC) (envelope-from julian@elischer.org) Received: from utility-0.aerioconnect.net (utility-0.aerioconnect.net [216.240.32.11]) by mx1.freebsd.org (Postfix) with ESMTP id D01038FC13 for ; Fri, 8 Jan 2010 17:38:23 +0000 (UTC) Received: from idiom.com (mx0.idiom.com [216.240.32.160]) by utility-0.aerioconnect.net (8.13.1/8.13.1) with ESMTP id o08HcHai019206; Fri, 8 Jan 2010 09:38:17 -0800 X-Client-Authorized: MaGic Cook1e X-Client-Authorized: MaGic Cook1e X-Client-Authorized: MaGic Cook1e X-Client-Authorized: MaGic Cook1e Received: from julian-mac.elischer.org (h-67-100-89-137.snfccasy.static.covad.net [67.100.89.137]) by idiom.com (Postfix) with ESMTP id D5C362D6012; Fri, 8 Jan 2010 09:38:16 -0800 (PST) Message-ID: <4B476D88.3080300@elischer.org> Date: Fri, 08 Jan 2010 09:38:16 -0800 From: Julian Elischer User-Agent: Thunderbird 2.0.0.23 (Macintosh/20090812) MIME-Version: 1.0 To: Julian Elischer , Pieter de Goeje , freebsd-hackers@freebsd.org, shrivatsan References: <5a13b8941001061349m701d17fbl489ec8cf883e8c3c@mail.gmail.com> <201001070017.36855.pieter@degoeje.nl> <4B452A5D.4000208@elischer.org> <20100108170338.GC52442@acme.spoerlein.net> In-Reply-To: <20100108170338.GC52442@acme.spoerlein.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Cc: Subject: Re: Question regarding memory disks X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 08 Jan 2010 17:38:24 -0000 Ulrich Spörlein wrote: > On Wed, 06.01.2010 at 16:27:09 -0800, Julian Elischer wrote: >> Pieter de Goeje wrote: >>> Because when you "erase" something, all it does is unlink (delete the >>> reference to) the data. So there is currently no way the memory disk can free >>> the memory associated with the data. That is also why you should normally use >>> swap backed memory disks instead, or use tmpfs. These can return memory to >>> the system. >>> >>> The ability of the filesystem to mark certain blocks as "erased" is important >>> not only for memory disks but also for solid state drives. It is a feature >>> UFS2 is currently lacking unfortunately. >> but is being worked on > > Will this automagically work for md(4) backed UFS2 file-systems? Is this > also being worked on? that will depend on md there are two patches out there that use the VFS DELETE command under UFS to free unused space. how that operation is handled depends on the lower level. Disclaimer: I have seen the patches but are not using them. I believe Mav and Jeff have both looked at this and Kirk showed a path that was similar to Jeff's. > > Regards, > Uli