From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f198.google.com (mail-qt0-f198.google.com [209.85.216.198]) by kanga.kvack.org (Postfix) with ESMTP id F22B46B0253 for ; Wed, 18 Jan 2017 10:38:57 -0500 (EST) Received: by mail-qt0-f198.google.com with SMTP id q3so11524874qtf.4 for ; Wed, 18 Jan 2017 07:38:57 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id f15si446056qta.220.2017.01.18.07.38.56 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 18 Jan 2017 07:38:57 -0800 (PST) Date: Wed, 18 Jan 2017 17:38:53 +0200 From: "Michael S. Tsirkin" Subject: Re: [PATCH v6 kernel 0/5] Extend virtio-balloon for fast (de)inflating & fast live migration Message-ID: <20170118173139-mutt-send-email-mst@kernel.org> 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-Disposition: inline In-Reply-To: <2a32f616-25a8-ba5a-f74c-d619fc8ab333@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: David Hildenbrand Cc: Liang Li , kvm@vger.kernel.org, virtio-dev@lists.oasis-open.org, qemu-devel@nongnu.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, amit.shah@redhat.com, dave.hansen@intel.com, cornelia.huck@de.ibm.com, pbonzini@redhat.com, aarcange@redhat.com, dgilbert@redhat.com, quintela@redhat.com On Wed, Jan 18, 2017 at 11:09:30AM +0100, David Hildenbrand wrote: > 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. As long as the interface is similar, it seems to make sense for me - why invent a completely new device that looks very much like the old one? So this boils down to whether the speedup patches are merged. > -- > > David -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org