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

[Pavel Butsykin <pbutsykin@virtuozzo.com>]

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.

> * 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
>