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SubjectRe: checkpoint/restart ABI


Jeremy Fitzhardinge wrote:
> Dave Hansen wrote:
>>>> I'm not sure what you mean by "closed files". Either the app has a fd,
>>>> it doesn't, or it is in sys_open() somewhere. We have to get the app
>>>> into a quiescent state before we can checkpoint, so we basically just
>>>> say that we won't checkpoint things that are *in* the kernel.
>>>>
>>> It's common for an app to write a tmp file, close it, and then open it a
>>> bit later expecting to find the content it just wrote. If you
>>> checkpoint-kill it in the interim, reboot (clearing out /tmp) and then
>>> resume, then it will lose its tmp file. There's no explicit connection
>>> between the process and its potential working set of files.
>>>
>> I respectfully disagree. The number one prerequisite for
>> checkpoint/restart is isolation. Xen just happens to get this for free.
>>
>
> (I don't have my Xen hat on at all for this thread.)
>
>> So, instead of saying that there's no explicit connection between the
>> process and its working set, ask yourself how we make a connection.
>>
>> In this case, we can do it with a filesystem (mount) namespace. Each
>> container that we might want to checkpoint must have its writable
>> filesystems contained to a private set that are not shared with other
>> containers. Things like union mounts would help here, but aren't
>> necessarily required. They just make it more efficient.
>>
>
> We were dealing with checkpointing random sets of processes, and that
> posed all sorts of problems. Filesystem namespace was one, the pid
> namespace was another. Doing checkpointing at the container-level
> granularity definitely solves a lot of problems.
>
>>>> Is there anything specific you are thinking of that particularly worries
>>>> you? I could write pages on the list you have there.
>>>>
>>> No, that's the problem; it all worries me. It's a big problem space.
>>>
>> It's almost as big of a problem as trying to virtualize entire machines
>> and expecting them to run as fast as native. :)
>>
>
> No, it's much harder. Hardware is relatively simple and immutable
> compared to kernel and process state ;)
>
>> Cool! I didn't know you guys did the IRIX implementation. I'm sure you
>> guys got a lot farther than any of us are. Did you guys ever write any
>> papers or anything on it? I'd be interested in more information.
>>
>
> Yeah, there was a paper, but it looks like the internet has lost it. It
> was at
> http://www.csu.edu.au/special/conference/apwww95/.papers95/cmaltby/cmaltby.ps
> http://www.csu.edu.au/special/conference/apwww95/sept-all.html has
> mention of the paper.
>

you can find it here:

http://ertos.nicta.com.au/publications/papers/Maltby_Chubb_95.pdf

Oren.



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