From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:43443) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Ui3XW-00087A-NU for qemu-devel@nongnu.org; Thu, 30 May 2013 10:09:20 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Ui3XR-0000zv-Sx for qemu-devel@nongnu.org; Thu, 30 May 2013 10:09:14 -0400 Message-ID: <51A75D73.3020805@redhat.com> Date: Thu, 30 May 2013 16:08:51 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <51A7036A.3050407@ozlabs.ru> <51A7049F.6040207@redhat.com> <51A70B3D.90609@ozlabs.ru> <51A71705.6060009@kamp.de> <51A74D79.7040204@redhat.com> <51A7564D.5090202@ozlabs.ru> In-Reply-To: <51A7564D.5090202@ozlabs.ru> Content-Type: text/plain; charset=KOI8-R Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] broken incoming migration List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexey Kardashevskiy Cc: "qemu-ppc@nongnu.org" , Peter Lieven , "qemu-devel@nongnu.org" , David Gibson Il 30/05/2013 15:38, Alexey Kardashevskiy ha scritto: >>> does this problem only occur on pseries emulation? >> >> Probably not. On a PC, it would occur if you had 4K of zeros in the >> source BIOS but not in the destination BIOS. When you reboot, the BIOS >> image is wrong. >> >>> not sending zero pages is not only a performance benefit it also makes >>> overcomitted memory usable. the madv_dontneed seems to kick in asynchronously >>> and memory is not available immediately. >> >> You could also scan the page for nonzero values before writing it. > > Scan where? On the source? It is there already. On the destination? Won't > just trying to read a page kill all effect from MADV_DONTNEED? No, zero pages are handled with special copy-on-write magic by the kernel. :) So, reading works but writing doesn't. Paolo