linux-kernel - Re: [PATCH v25 0/2] Virtio-balloon: support free page reporting

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Date:   Fri, 02 Feb 2018 20:48:39 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     virtio-dev@...ts.oasis-open.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-mm@...ck.org, mhocko@...nel.org, akpm@...ux-foundation.org,
        pbonzini@...hat.com, liliang.opensource@...il.com,
        yang.zhang.wz@...il.com, quan.xu0@...il.com, nilal@...hat.com,
        riel@...hat.com
Subject: Re: [PATCH v25 0/2] Virtio-balloon: support free page reporting

On 02/02/2018 03:15 AM, Michael S. Tsirkin wrote:
> On Thu, Jan 25, 2018 at 05:14:04PM +0800, Wei Wang wrote:
>> This patch series is separated from the previous "Virtio-balloon
>> Enhancement" series. The new feature, VIRTIO_BALLOON_F_FREE_PAGE_HINT,
>> implemented by this series enables the virtio-balloon driver to report
>> hints of guest free pages to the host. It can be used to accelerate live
>> migration of VMs. Here is an introduction of this usage:
>>
>> Live migration needs to transfer the VM's memory from the source machine
>> to the destination round by round. For the 1st round, all the VM's memory
>> is transferred. From the 2nd round, only the pieces of memory that were
>> written by the guest (after the 1st round) are transferred. One method
>> that is popularly used by the hypervisor to track which part of memory is
>> written is to write-protect all the guest memory.
>>
>> The second feature enables the optimization of the 1st round memory
>> transfer - the hypervisor can skip the transfer of guest free pages in the
>> 1st round. It is not concerned that the memory pages are used after they
>> are given to the hypervisor as a hint of the free pages, because they will
>> be tracked by the hypervisor and transferred in the next round if they are
>> used and written.
> Could you post performance numbers please?

Yes, it was posted here https://lkml.org/lkml/2018/1/25/698

I just changed the host side to poll the vq so that we don't need kick 
in the driver, it works pretty well. I'll test a little bit more and 
post out a new version with new performance numbers attached in the 
cover letter.

Best,
Wei