Re: Process migration and persistence

[Daniel W. <wad...@gm...>]

The more I think about this (and experiment) the more I think that process
hibernation is quite feasible in Genode (assuming reconstruction of state
in dependent services) and much easier than in a traditional UNIX based
systems where process state is thrown around and difficult to track/get to
without kernel help.  Being able to serialize processes (and identify all
state belonging to a process) could be a real differentiator for Genode in
the long run.  Such a capability would have direct relevance to scalability
and future storage class memories.

Daniel


On Thu, Mar 17, 2016 at 11:41 AM, Daniel Waddington <wad...@gm...>
wrote:

> Hi Norman,
> Thanks for the extensive reply (I expected no less from you ;-)). I need
> to think on your input. I don't have a concrete use-case yet, I'm simply
> thinking about fast time-multiplexing of huge numbers (e.g., millions) of
> application instances that can't all be held in memory at once and can't be
> combined.  I'm thinking about how Genode/microkernels relates to unikernels
> and mirage OS/jitsu objectives.
>
> Daniel
>
>
> On Thu, Mar 17, 2016 at 10:07 AM, Norman Feske <
> nor...@ge...> wrote:
>
>> Hi Daniel,
>>
>> great to see you back in Genode land! :-)
>>
>> > I'd like to be able to freeze a process (PD or even a vmm), make it
>> > persistent, and unfreeze at some later point in time.  Does anyone have
>> > suggestions/pointers on how to do this?
>>
>> This does not work out of the box but I see two principal approaches:
>>
>> 1) You can run the to-be-frozen program as a child of a custom runtime
>>    environment that intercepts the program's PD, CPU, RM, and RAM
>>    sessions. So the environment knows everything that goes on within
>>    the program. This is what the Noux runtime is doing. Thanks to
>>    this approach, we are able to implement fork on top of Genode. This
>>    is actually very similar to what you want to achieve. Instead of
>>    replicating the forking program, however, you would serialize/
>>    unserialize this information. That said, there are some constraints
>>    worth noting. Most importantly, the new process "forgets" all its
>>    capabilities. So it must re-obtain them in order to work as
>>    expected. In Noux processes, this is possible because we hide
>>    Genode capabilities behind the POSIX API. So only the libc deals
>>    with capabilities and can actively re-establish them after the
>>    fork.
>>
>>    Another example to look at is the GDB monitor. Similar to Noux,
>>    it intercepts the said core services. But it uses them to inspect
>>    and control the to-be-debugged program.
>>
>> 2) Our general agenda is to create components as mere state
>>    machines that are fed with state (e.g., using ROM sessions)
>>    and propagate their results (e.g., using Report sessions). Since
>>    such components don't contain unrecoverable internal state,
>>    we can just kill and restart them. When presented with the
>>    same imported state (aka ROM sessions) after the restart, they
>>    end up in the same internal state as before. A practical
>>    example of this approach is the way, the window decorator
>>    interacts with the window manager in the Turmvilla scenario.
>>    Here, we can dynamically replace one decorator component by
>>    another implementation while retaining all of the window layout.
>>
>>    This approach just defines the problem away, which I find very
>>    nice. :-)
>>
>> For complex monolithic applications with comprehensive internal state,
>> there is the further option to run it with a VM (i.e., VirtualBox).
>> Although we haven't tried it with our port, VirtualBox comes with the
>> ability to suspend a VM to a file. I think this feature could be enabled
>> in our version of VirtualBox without too much trouble.
>>
>> Can you share more details about your use case?
>>
>> Cheers
>> Norman
>>
>> --
>> Dr.-Ing. Norman Feske
>> Genode Labs
>>
>> http://www.genode-labs.com · http://genode.org
>>
>> Genode Labs GmbH · Amtsgericht Dresden · HRB 28424 · Sitz Dresden
>> Geschäftsführer: Dr.-Ing. Norman Feske, Christian Helmuth
>>
>>
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