From: Theodore Tso Subject: Re: zero out blocks of freed user data for operation a virtual machine environment Date: Mon, 25 May 2009 08:03:20 -0400 Message-ID: <20090525120320.GA25908@mit.edu> References: <20090524170045.GC24753@cip.informatik.uni-erlangen.de> <20090524101551.57b706e9@infradead.org> <20090524173933.GD24753@cip.informatik.uni-erlangen.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: Thomas Glanzmann , Arjan van de Ven , tytso@thunk.org, LKML , linux-ext4@vger.kernel.org Return-path: Received: from thunk.org ([69.25.196.29]:46077 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751681AbZEYMDo (ORCPT ); Mon, 25 May 2009 08:03:44 -0400 Content-Disposition: inline In-Reply-To: <20090524173933.GD24753@cip.informatik.uni-erlangen.de> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Sun, May 24, 2009 at 07:39:33PM +0200, Thomas Glanzmann wrote: > Hello, > > > > tunable feature that zeroes our free data > > > wouldn't it be better if the VM's would just support the TRIM command? > > the resources available to me indicate that the TRIM command is a not > yet standarized command targeted at SSD disks to indicate free disk > space. Does ext3/4 trigger a block device layer call that could result > in a TRIM command? Yes, it does, sb_issue_discard(). So if you wanted to hook into this routine with a function which issued calls to zero out blocks, it would be easy to create a private patch. - Ted