linux-kernel - Re: [PATCH v34 0/4] Virtio-balloon: support free page reporting

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Date:   Sat, 30 Jun 2018 12:31:19 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     virtio-dev@...ts.oasis-open.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-mm@...ck.org, mst@...hat.com, mhocko@...nel.org,
        akpm@...ux-foundation.org
CC:     torvalds@...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,
        peterx@...hat.com
Subject: Re: [PATCH v34 0/4] Virtio-balloon: support free page reporting

On 06/25/2018 08:05 PM, 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.
>
> This feature enables the optimization by skipping the transfer of guest
> free pages during VM live migration. 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 subsequent round if they are used and written.
>
> * Tests
> - Test Environment
>      Host: Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz
>      Guest: 8G RAM, 4 vCPU
>      Migration setup: migrate_set_speed 100G, migrate_set_downtime 2 second
>
> - Test Results
>      - Idle Guest Live Migration Time (results are averaged over 10 runs):
>          - Optimization v.s. Legacy = 284ms vs 1757ms --> ~84% reduction

According to Michael's comments, add one more set of data here:

Enabling page poison with value=0, and enable KSM.

The legacy live migration time is 1806ms (averaged across 10 runs), 
compared to the case with this optimization feature in use (i.e. 284ms), 
there is still around ~84% reduction.


Best,
Wei