From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=36397 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PKM5m-0002jI-SK for qemu-devel@nongnu.org; Sun, 21 Nov 2010 21:25:19 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PKM5l-0006j9-OQ for qemu-devel@nongnu.org; Sun, 21 Nov 2010 21:25:18 -0500 Received: from [222.73.24.84] (port=50260 helo=song.cn.fujitsu.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PKM5l-0006iE-AH for qemu-devel@nongnu.org; Sun, 21 Nov 2010 21:25:17 -0500 Message-ID: <4CE9D4A1.6050900@cn.fujitsu.com> Date: Mon, 22 Nov 2010 10:25:37 +0800 From: Wen Congyang MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH] stop the iteration when too many pages is transferred References: <4CE49053.3000608@cn.fujitsu.com> <4CE7313B.1070103@codemonkey.ws> In-Reply-To: <4CE7313B.1070103@codemonkey.ws> Content-Type: text/plain; charset=GB2312 Content-Transfer-Encoding: quoted-printable List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: qemu-devel At 2010=C4=EA11=D4=C220=C8=D5 10:23, Anthony Liguori Write: > On 11/17/2010 08:32 PM, Wen Congyang wrote: >> When the total sent page size is larger than max=5Ffactor >> times of the size of guest OS's memory, stop the >> iteration. >> The default value of max=5Ffactor is 3. >> >> This is similar to XEN. >> >> >> Signed-off-by: Wen Congyang >> =20 >=20 > I'm strongly opposed to doing this. I think Xen gets this totally wrong. >=20 > Migration is a contract. When you set the stop time, you're saying that > you want only want the guest to experience a fixed amount of downtime. > Stopping the guest after some arbitrary number of iterations makes the > downtime non-deterministic. With a very large guest, this could wreak > havoc causing dropped networking connections, etc. >=20 Thanks for your comment. As a developer, I know the downtime. But as a user, he does not know the downtime. When he migrates a very large guest lively without setting the stop time, he does not say "I want the guest to experience a fixed amount of downtime", he only wants to migrate the guest in a short time, the migration should be done during some minutes, not ever for ever. If we set the stop time too larger, this could also wreak havoc causing dropped networking connections, etc. I think we can do it as the following: 1. If the user does not set the stop time, we should complete the migration in a short time. 2. If the user sets the stop time, we do it as now. > It's totally unsafe. >=20 > If a management tool wants this behavior, they can set a timeout and > explicitly stop the guest during the live migration. IMHO, such a > management tool is not doing it's job properly but it still can be > implemented. >=20 > Regards, >=20 > Anthony Liguori >=20