From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33362) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eZLrX-0006lb-7F for qemu-devel@nongnu.org; Wed, 10 Jan 2018 14:16:35 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eZLrW-00073H-6O for qemu-devel@nongnu.org; Wed, 10 Jan 2018 14:16:35 -0500 Received: from mail-wm0-x231.google.com ([2a00:1450:400c:c09::231]:37471) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1eZLrW-00072h-0O for qemu-devel@nongnu.org; Wed, 10 Jan 2018 14:16:34 -0500 Received: by mail-wm0-x231.google.com with SMTP id f140so1026328wmd.2 for ; Wed, 10 Jan 2018 11:16:33 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20180109195517.GD2708@work-vm> References: <20180109153538.GC1197@stefanha-x1.localdomain> <20180109195517.GD2708@work-vm> From: Stefan Hajnoczi Date: Wed, 10 Jan 2018 19:16:32 +0000 Message-ID: Content-Type: text/plain; charset="UTF-8" Subject: Re: [Qemu-devel] Some question about savem/qcow2 incremental snapshot List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Dr. David Alan Gilbert" Cc: "He, Junyan" , "qemu-devel@nongnu.org" , Juan Quintela , John Snow On Tue, Jan 9, 2018 at 7:55 PM, Dr. David Alan Gilbert wrote: >> Certain guest operations like rebooting or zeroing memory will defeat >> the incremental guest RAM snapshot feature. It's worth thinking about >> these cases to make sure this feature would be worth it in real use >> cases. > > But those probably wouldn't upset an NVDimm? If the guest dirties all RAM then the incremental snapshot feature degrades to a full snapshot. I'm asking if there are common operations where that happens. I seem to remember Windows guests zero all pages on cold boot. Maybe that's not the case anymore. Worth checking before embarking on this feature because it could be a waste of effort if it turns out real-world guests dirty all memory in common cases.