Re: [Qemu-devel] [PATCH v2 0/3] migration capability to discard the migrated ram pages

[Pavel Butsykin <pbutsykin@virtuozzo.com>]

On 07.03.2017 16:56, Dr. David Alan Gilbert wrote:
> * Pavel Butsykin (pbutsykin@virtuozzo.com) wrote:
>> On 14.02.2017 17:02, Dr. David Alan Gilbert wrote:
>>> Hi Pavel,
>>>     I was curious, having merged this, how you're using postcopy; do you switch
>>> into postcopy mode immediately or wait until the first sync or what?
>>> Do you find yourself in postcopy mode long enough that it's worth
>>> doing the release?  If so on what size VMs are you working with?
>>>
>>> Dave
>>
>> Hi Dave,
>> I'm sorry it took so long, I was on vacation. And thanks for the quick
>> review and merge!
>>
>> We want to use this function to update Qemu without rebooting VMs. It
>> looks like a local migration on the same host. Now, switching into
>> postcopy mode is done immediately, the size of VMs can be very
>> different.
>
> Thanks! Do you have libvirt magic to do that update?

Yes, there are patches that add a flag "--local" for migration. The
flag adds start incoming VM and other magic about replacement source on
destination.

> Dave
>
>>> * Pavel Butsykin (pbutsykin@virtuozzo.com) wrote:
>>>> This feature frees the migrated memory on the source during postcopy-ram
>>>> migration. In the second step of postcopy-ram migration when the source vm
>>>> is put on pause we can free unnecessary memory. It will allow, in particular,
>>>> to start relaxing the memory stress on the source host in a load-balancing
>>>> scenario.
>>>>
>>>> Changes from v1:
>>>> - changed name of the interfaces (discard to release)
>>>> - fix make check error
>>>> - add more comments to qemu_iovec_release_ram()
>>>> - rebase on "Postcopy: Hugepage support" (David's patch series)
>>>> - removed ram_discard_page for xbzrle
>>>> - fix erroneous release memory in complete precopy (tie release-ram to postcopy)
>>>>
>>>> Pavel Butsykin (3):
>>>>     migration: add MigrationState arg for ram_save_/compressed_/page()
>>>>     add 'release-ram' migrate capability
>>>>     migration: discard non-dirty ram pages after the start of postcopy
>>>>
>>>>    include/migration/migration.h |  2 ++
>>>>    include/migration/qemu-file.h |  3 ++-
>>>>    migration/migration.c         | 13 ++++++++++
>>>>    migration/qemu-file.c         | 59 ++++++++++++++++++++++++++++++++++++++-----
>>>>    migration/ram.c               | 56 ++++++++++++++++++++++++++++++++++------
>>>>    qapi-schema.json              |  5 +++-
>>>>    6 files changed, 121 insertions(+), 17 deletions(-)
>>>>
>>>> --
>>>> 2.11.0
>>>>
>>>>
>>> --
>>> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>>>
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>