On 05.02.20 09:54, Wang, Wei W wrote:

On Wednesday, February 5, 2020 4:19 PM, David Hildenbrand wrote:

quoted

Yes, I agree with you. Yet, I am thinking about one
(unlikely?impossible?) scenario. Can you refresh my brain why that cannot
happen (IOW, why we don't have to wait for the host to process the
request)?

1. Guest allocates a page and sends it to the host.
2. Shrinker gets active and releases that page again.
3. Some user in the guest allocates and modifies that page. After that, it is
done using that page for the next hour.
4. The host processes the request and clears the bit in the dirty bitmap.
5. The guest is being migrated by the host. The modified page is not being
migrated.

Whenever the guest modifies a page during migration, it will be captured by the
dirty logging and the hypervisor will send the dirtied the page in the following round.

Please explain why the steps I outlined don't apply esp. in the last
round. Your general statement does not explain why this race can't happen.

-- 
Thanks,

David / dhildenb