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Date: Fri, 14 Apr 2017 10:28:32 +0800 From: Wei Wang <wei.w.wang@...el.com> To: "Michael S. Tsirkin" <mst@...hat.com>, Matthew Wilcox <willy@...radead.org> CC: virtio-dev@...ts.oasis-open.org, linux-kernel@...r.kernel.org, qemu-devel@...gnu.org, virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org, linux-mm@...ck.org, david@...hat.com, dave.hansen@...el.com, cornelia.huck@...ibm.com, akpm@...ux-foundation.org, mgorman@...hsingularity.net, aarcange@...hat.com, amit.shah@...hat.com, pbonzini@...hat.com, liliang.opensource@...il.com Subject: Re: [PATCH v9 0/5] Extend virtio-balloon for fast (de)inflating & fast live migration On 04/14/2017 09:50 AM, Michael S. Tsirkin wrote: > On Thu, Apr 13, 2017 at 01:44:11PM -0700, Matthew Wilcox wrote: >> On Thu, Apr 13, 2017 at 05:35:03PM +0800, Wei Wang wrote: >>> 2) transfer the guest unused pages to the host so that they >>> can be skipped to migrate in live migration. >> I don't understand this second bit. You leave the pages on the free list, >> and tell the host they're free. What's preventing somebody else from >> allocating them and using them for something? Is the guest semi-frozen >> at this point with just enough of it running to ask the balloon driver >> to do things? > There's missing documentation here. > > The way things actually work is host sends to guest > a request for unused pages and then write-protects all memory. > > So guest isn't frozen but any changes will be detected by host. > Probably it's better to say " transfer the info about the guest unused pages to the host so that the host gets a chance to skip the transfer of the unused pages during live migration". Best, Wei
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