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

[Pavel Butsykin <pbutsykin@virtuozzo.com>]

On 07.03.2017 17:46, Dr. David Alan Gilbert wrote:
> * Pavel Butsykin (pbutsykin@virtuozzo.com) wrote:
>> 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.
>
> Nice; are those posted to libvirt's list somewhere?

Not yet, but we're going to do it.

> Dave
>
>>> 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
>>>
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>