[CRIU] Lazy-restore design discussion - round 2

[Pavel Emelyanov]

On 04/18/2016 06:35 PM, Adrian Reber wrote:
> On Mon, Apr 18, 2016 at 06:28:01PM +0300, Pavel Emelyanov wrote:
>> On 04/18/2016 05:28 PM, Mike Rapoport wrote:
>>> On Mon, Apr 18, 2016 at 02:24:21PM +0300, Pavel Emelyanov wrote:
>>>> On 04/18/2016 01:10 PM, Mike Rapoport wrote:
>>>>> On Mon, Apr 18, 2016 at 12:31:14PM +0300, Pavel Emelyanov wrote:
>>>>>> On 04/18/2016 10:46 AM, Adrian Reber wrote:
>>>>>>> It seems we have reached some kind of agreement and therefore
>>>>>>> I am trying to summarize, from my point of view, our current discussion
>>>>>>> results.
>>>>>>
>>>>>> Thanks for keeping track of this :)
>>>>>
>>>>> Adrian, you've beat me on this :)
>>>>>  
>>>>>>>  * The UFFD daemon does not need a checkpoint directory to run, all
>>>>>>>    required information will be transferred over the network.
>>>>>>>    e.g. PID and pages
>>>>>>
>>>>>> I would still read process tree from images dir.
>>>>>
>>>>> +1
>>>>>  
>>>>>>>  * The page-server protocol needs to be extended to transfer the
>>>>>>>    lazy-restore pages list from the source system to the UFFD daemon.
>>>>>>
>>>>>> You mean the pagemap-s? But we have the images dir on the destination node,
>>>>>> uffd can read this information from there as well.
>>>>>
>>>>> The means that dump side should be teached to split pagemap creation and
>>>>> actual page dump, right?
>>>>
>>>> Right, but it's already such. Is it?
>>>
>>> Well, I probably should have phrased it "page-xfer should be refactored to
>>> support split between pagemap and actual pages dump"...
>>
>> Probably :) But in page-xfer we already have ->write_pagemap and ->write_pages.
>> Do you mean something more than this?
> 
> My original point "The page-server protocol needs to be extended ..."
> seems irrelevant now, as the uffd daemon will have access to the image
> directory. We probably need to differentiate between write_pages() for
> lazy-pages and write_pages() for non-lazy-pages, right?

Likely, but the page xfer protocol already knows pages vs holes, so adding
lazy pages should easy.

-- Pavel