Messages in this thread | | | Date | Tue, 12 Aug 2008 10:04:57 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: checkpoint/restart ABI |
| |
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.
J
| |