[CRIU] Criu Page server on source

[Radostin Stoyanov]

On 03/04/2021 19:26, Adrian Reber wrote:
> On Thu, Apr 01, 2021 at 04:08:33PM +0100, DALLEL KHEZZANE wrote:
>>   Hello ,
>>
>> on the Documentation this figure, Criu-memory-wflow.png
>> <https://criu.org/w/images/3/39/Criu-memory-wflow.png> (attached below)
>> showcasing the memory transfer workflow in each of these cases:
>> - classic flow
>> - page server on destination
>> - page server on source
>> - lazy migration
>> I tried these scenarios to compare downtime, but in the case of page server
>> on source it is shown on the figure  that it can be done without writing to
>> disk at all.correct me if i misunderstood.
> This sounds strange. Why do you start the page server on the source side
> of the migration? The page server should be running on the destination
> side. This way it is possible for CRIU to directly transfer the memory
> pages over the network to the destination without writing the pages
> locally to disk.
>
>> after lauching page server on source then performing checkpoint with page
>> server on source,
>> how can i transfer the image pages in order to restore on destination
>> without writing to disk?
>> i don't understand this particular page-server on source workflow on the
>> figure what does the arrow with remote stand for?

As far as I understand, and perhaps it is not very clear, the figure 
describes the internal page-server implementation in CRIU.

As such, "page xfer" under "dump" refers to the part of the source code 
that sends memory pages to the destination side (see 
page_xfer_dump_pages() in criu/page-xfer.c). While in the legend this is 
described as "Page server on src", it represents functionality invoked 
by the "criu dump" command, not the "criu page-server" command.

I hope this helps.

> This sounds like a misunderstanding. The page server should run on the
> destination side of the migration.
>
> 		Adrian
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