From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Li, Liang Z" Subject: RE: [PATCH v6 kernel 0/5] Extend virtio-balloon for fast (de)inflating & fast live migration Date: Wed, 18 Jan 2017 13:29:59 +0000 Message-ID: References: <1482303148-22059-1-git-send-email-liang.z.li@intel.com> <2a32f616-25a8-ba5a-f74c-d619fc8ab333@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <2a32f616-25a8-ba5a-f74c-d619fc8ab333@redhat.com> Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: David Hildenbrand , "kvm@vger.kernel.org" Cc: "aarcange@redhat.com" , "virtio-dev@lists.oasis-open.org" , "Hansen, Dave" , "linux-kernel@vger.kernel.org" , "mst@redhat.com" , "qemu-devel@nongnu.org" , "virtualization@lists.linux-foundation.org" , "linux-mm@kvack.org" , "amit.shah@redhat.com" , "pbonzini@redhat.com" , "dgilbert@redhat.com" List-Id: virtualization@lists.linuxfoundation.org > Am 21.12.2016 um 07:52 schrieb Liang Li: > > This patch set contains two parts of changes to the virtio-balloon. > > > > One is the change for speeding up the inflating & deflating process, > > the main idea of this optimization is to use {pfn|length} to present > > the page information instead of the PFNs, to reduce the overhead of > > virtio data transmission, address translation and madvise(). This can > > help to improve the performance by about 85%. > > > > Another change is for speeding up live migration. By skipping process > > guest's unused pages in the first round of data copy, to reduce > > needless data processing, this can help to save quite a lot of CPU > > cycles and network bandwidth. We put guest's unused page information > > in a {pfn|length} array and send it to host with the virt queue of > > virtio-balloon. For an idle guest with 8GB RAM, this can help to > > shorten the total live migration time from 2Sec to about 500ms in > > 10Gbps network environment. For an guest with quite a lot of page > > cache and with little unused pages, it's possible to let the guest > > drop it's page cache before live migration, this case can benefit from this > new feature too. > > I agree that both changes make sense (although the second change just > smells very racy, as you also pointed out in the patch description), however I > am not sure if virtio-balloon is really the right place for the latter change. > > virtio-balloon is all about ballooning, nothing else. What you're doing is using > it as a way to communicate balloon-unrelated data from/to the hypervisor. > Yes, it is also about guest memory, but completely unrelated to the purpose > of the balloon device. > > Maybe using virtio-balloon for this purpose is okay - I have mixed feelings > (especially as I can't tell where else this could go). I would like to get a second > opinion on this. > We have ever discussed the implementation for a long time, making use the current virtio balloon seems better than the other solutions and is recommended by Michael. Thanks! Liang > -- > > David