Re: Balloon pressuring page cache

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On 05.02.20 09:54, Wang, Wei W wrote:
> On Wednesday, February 5, 2020 4:19 PM, David Hildenbrand wrote:
>> 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





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