From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57686) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Utd0Q-0007mN-J7 for qemu-devel@nongnu.org; Mon, 01 Jul 2013 08:14:55 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Utd0P-0007hP-F1 for qemu-devel@nongnu.org; Mon, 01 Jul 2013 08:14:54 -0400 Received: from mail-wi0-x232.google.com ([2a00:1450:400c:c05::232]:50547) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UtcXx-0007S0-PW for qemu-devel@nongnu.org; Mon, 01 Jul 2013 07:45:29 -0400 Received: by mail-wi0-f178.google.com with SMTP id k10so2958156wiv.5 for ; Mon, 01 Jul 2013 04:45:29 -0700 (PDT) Date: Mon, 1 Jul 2013 13:45:26 +0200 From: Stefan Hajnoczi Message-ID: <20130701114526.GA5543@stefanha-thinkpad.redhat.com> References: <1369709437-24969-1-git-send-email-qiaonuohan@cn.fujitsu.com> <20130619134952.GE31475@stefanha-thinkpad.muc.redhat.com> <51C2667B.4030600@cn.fujitsu.com> <20130620085719.GA15672@stefanha-thinkpad.redhat.com> <51CBE58D.8080507@cn.fujitsu.com> <20130627085451.GB14351@stefanha-thinkpad.redhat.com> <51CCFB98.2020404@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51CCFB98.2020404@cn.fujitsu.com> Subject: Re: [Qemu-devel] [PATCH v4 0/9] Make 'dump-guest-memory' dump in kdump-compressed format List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Qiao Nuohan Cc: zhangxh@cn.fujitsu.com, qemu-devel@nongnu.org, lcapitulino@redhat.com, anderson@redhat.com, kumagai-atsushi@mxc.nes.nec.co.jp, afaerber@suse.de On Fri, Jun 28, 2013 at 10:57:28AM +0800, Qiao Nuohan wrote: > On 06/27/2013 04:54 PM, Stefan Hajnoczi wrote: > > > >The interesting question is how effective this approach is. If it's > >good enough then it would be a fairly simple modification to dump.c. > > I see, if excluding zero page in ELF can make a lot of size reduce, it's better > to choose this method. But think over the situation that kernel is on for a > long time, then few zero pages will be in memory, compression will do more work > to reduce size not excluding zero pages. So the approach is not always > effective. > > A test on a 1GB memory, and the machine is just on: > > size format method for reducing memory > > 1.1GB ELF no > 1.1GB kdump no > 227MB kdump with all zero pages excluded > 96MB kdump compressed with zero pages remained > 88MB kdump compressed with zero pages excluded > > excluding zero pages does some work, but compression seems to be more effective. [...] > >If it makes the code simpler and smaller it would be nice. > > That's the point. I will make the code simpler. I'm now convinced that kdump is worthwhile, thanks for providing data. It would be nice to see the flattened kdump approach. Stefan