Messages in this thread | | | Date | Wed, 20 Aug 2008 17:52:29 -0400 | From | Oren Laadan <> | Subject | Re: checkpoint/restart ABI |
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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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