[CRIU] zdtm: lazy pages arguments

[Mike Rapoport]

Hi,

On Thu, Sep 13, 2018 at 04:30:39PM +0100, Radostin Stoyanov wrote:
> Hi all,
> 
> I am trying to understand what is the difference between --lazy-pages,
> --lazy-migrate and --remote-lazy-pages arguments of zdtm.

--lazy-pages tests lazy restore from images. In this case dump works
"normally", restore skips the memory pages that can be handled on demand
and lazy-pages daemon handles the page faults and reads the memory contents
from the image files.

--remote-lazy-pages simulates post-copy memory migration. Here again, the
dump works "normally", but the lazy-pages daemon does not read data from
the image files but requests it "over the network" for the page-server. It
is the page-server that reads memory pages from the images and simulates
what 'dump --lazy-pages' wound have done.

--lazy-migrate actually does post-copy migration. It cannot run with the
host flavor because during post-copy migration the migrated tasks should
exist both on the source and the destination.

> Is it possible to combine them?

Well, they do overlap, but there are code paths that are tested only in one
of them.
Nothing comes to mind right now, but I remember that there were bugs that
showed up in one of the cases and didn't appear in others.



> --lazy-pages was introduced with
> https://github.com/checkpoint-restore/criu/commit/f59b45f
> 
>     zdtm: check lazy-pages
> 
> 
> --lazy-migrate was introduced with
> https://github.com/checkpoint-restore/criu/commit/d499aea
> 
>      zdtm: enable lazy migration testing
> 
> 
> The --lazy-migrate option allows testing of lazy migration when running ns
> or uns flavor.
> 
> --remote-lazy-pages was introduced with
> https://github.com/checkpoint-restore/criu/commit/c89a22a
> 
>      zdtm: simulate lazy migration with page server that can send pages
> 
>     Lazy migration requires both dumped and restored processes to coexist at
>     the same time. This breaks some basic assumptions in the zdtm design.
>     Simulation of lazy migration with the page server allows testing most of
>     the involved code paths without major intervention into zdtm
>     infrastructure.
> 
> 
> Thanks,
> Radostin
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-- 
Sincerely yours,
Mike.