From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57916) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aLMwB-0001Uv-Un for qemu-devel@nongnu.org; Mon, 18 Jan 2016 22:26:32 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aLMw6-0005bb-Vs for qemu-devel@nongnu.org; Mon, 18 Jan 2016 22:26:31 -0500 Received: from szxga03-in.huawei.com ([119.145.14.66]:31011) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aLMw5-0005bH-V7 for qemu-devel@nongnu.org; Mon, 18 Jan 2016 22:26:26 -0500 References: <1452851297-11198-1-git-send-email-liang.z.li@intel.com> <5698C735.3020409@huawei.com> <569CA9CC.80603@huawei.com> <569DA952.3090501@huawei.com> From: Hailiang Zhang Message-ID: <569DAC95.8080704@huawei.com> Date: Tue, 19 Jan 2016 11:25:09 +0800 MIME-Version: 1.0 In-Reply-To: <569DA952.3090501@huawei.com> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] migration: not send zero page header in ram bulk stage List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Li, Liang Z" , "qemu-devel@nongnu.org" Cc: "amit.shah@redhat.com" , "pbonzini@redhat.com" , peter.huangpeng@huawei.com, "dgilbert@redhat.com" , "quintela@redhat.com" On 2016/1/19 11:11, Hailiang Zhang wrote: > On 2016/1/19 9:26, Li, Liang Z wrote: >>> On 2016/1/15 18:24, Li, Liang Z wrote: >>>>> It seems that this patch is incorrect, if the no-zero pages are >>>>> zeroed again during !ram_bulk_stage, we didn't send the new zeroed >>>>> page, there will be an error. >>>>> >>>> >>>> If not in ram_bulk_stage, still send the header, could you explain why it's >>> wrong? >>>> >>>> Liang >>>> >>> >>> I have made a mistake, and yes, this patch can speed up the live migration >>> time, especially when there are many zero pages, it will be more obvious. >>> I like this idea. Did you test it with postcopy ? Does it break postcopy ? >>> >> >> Not yet, I saw Dave's comment's, it will beak post copy, it's not hard to fix this. >> A more important thing is Paolo's comments, I don't know in which case this patch will break LM. Do you have any idea about this? >> Hope that QEMU don't write data to the block 'pc.ram'. >> > > Paolo is right, for VM in destination, QEMU may write VM's memory before VM starts. > So your assumption that "VM's RAM pages are initialized to zero" is incorrect. > This patch will break LM. > Actually, someone has done like that before and cause a migration bug, See commit f1c72795af573b24a7da5eb52375c9aba8a37972, and the fixing patch is commit 9ef051e5536b6368a1076046ec6c4ec4ac12b5c6 Revert "migration: do not sent zero pages in bulk stage" >> Liang >> >>> Thanks, >>> zhanghailiang >>> >> >> . >> >