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Re: [Qemu-devel] [PATCH v2 0/3] virtio-balloon: free page hint reporting

From: Wei Wang
Subject: Re: [Qemu-devel] [PATCH v2 0/3] virtio-balloon: free page hint reporting support
Date: Fri, 09 Feb 2018 11:10:25 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

On 02/09/2018 04:15 AM, Dr. David Alan Gilbert wrote:
* Wei Wang (address@hidden) wrote:
This is the deivce part implementation to add a new feature,
VIRTIO_BALLOON_F_FREE_PAGE_HINT to the virtio-balloon device. The device
receives the guest free page hints from the driver and clears the
corresponding bits in the dirty bitmap, so that those free pages are
not transferred by the migration thread to the destination.

Please see the driver patch link for test results:
Hi Wei,
    I'll look at the code a bit more - but first some more basic
questions on that lkml post:

     a) The idle guest time thing is a nice result; can you just state
        what the host was, speed of connection, and what other options
        you were using?

     b) The workload test, the one with the kernel compile; you list
        the kernel compile time but don't mention any changes in the
        migration times of the ping-pong; can you give those times as

     c) What's your real workload that this is aimed at?
        Is it really for people migrating idle VMs - or do you have some
        NFV application in mind, if so why not include a figure for

Hi Dave,

Thanks for joining the review. Please see below info.

a) Environment info
    - Host:
        - Physical CPU: Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz
        - kernel: 3.10.0

    - Guest:
        - kernel: 4.15.0
- QEMU setup: -cpu host -M pc -smp 4,threads=1,sockets=1 -m 8G --mem-prealloc -realtime mlock=on -balloon virtio,free-page-hint=true

    - Migration setup:
        - migrate_set_speed 0
        - migrate_set_downtime 0.01  (10ms)

b) Michael asked the same question on the kernel patches, I'll reply there with you cc-ed, so that kernel maintainers can also see it. Btw, do you have any other workloads you would suggest to have a try?

c) This feature is requested by many customers (e.g. general cloud vendors). It's for general use cases. As long as the guest has free memory, it will benefit from this optimization when doing migration. It's not specific for NFV usages, but for sure NFV will also benefit from this feature if we think about service chaining, where multiple VMs need to co-work with each other. In that case, migrating one VM will just break the working model, which means we will need to migrate all the VMs. A shorter migration time will be very helpful.


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