On 05.01.2021 22:36, Peter Xu wrote:
> On Thu, Dec 17, 2020 at 07:57:07PM +0300, Andrey Gruzdev wrote:
>> This patch series is a kind of 'rethinking' of Denis Plotnikov's ideas he's
>> implemented in his series '[PATCH v0 0/4] migration: add background snapshot'.
>>
>> Currently the only way to make (external) live VM snapshot is using existing
>> dirty page logging migration mechanism. The main problem is that it tends to
>> produce a lot of page duplicates while running VM goes on updating already
>> saved pages. That leads to the fact that vmstate image size is commonly several
>> times bigger then non-zero part of virtual machine's RSS. Time required to
>> converge RAM migration and the size of snapshot image severely depend on the
>> guest memory write rate, sometimes resulting in unacceptably long snapshot
>> creation time and huge image size.
>>
>> This series propose a way to solve the aforementioned problems. This is done
>> by using different RAM migration mechanism based on UFFD write protection
>> management introduced in v5.7 kernel. The migration strategy is to 'freeze'
>> guest RAM content using write-protection and iteratively release protection
>> for memory ranges that have already been saved to the migration stream.
>> At the same time we read in pending UFFD write fault events and save those
>> pages out-of-order with higher priority.
>>
>> How to use:
>> 1. Enable write-tracking migration capability
>>     virsh qemu-monitor-command <domain> --hmp migrate_set_capability.
>> track-writes-ram on
>>
>> 2. Start the external migration to a file
>>     virsh qemu-monitor-command <domain> --hmp migrate exec:'cat > ./vm_state'
>>
>> 3. Wait for the migration finish and check that the migration has completed.
>> state.
> For the rest patches:
>
> Acked-by: Peter Xu <peterx@redhat.com>
>
> Dave, considering the live snapshot series has been dangling for quite some
> time upstream (starting from Denis's work), do you have plan to review/merge it
> in the near future?
>
> I believe there're still quite a few things missing, but imho most of them
> should be doable on top too.
>
> Thanks!
>
Thanks, Peter!

-- 
Andrey Gruzdev, Principal Engineer
Virtuozzo GmbH  +7-903-247-6397
                 virtuzzo.com