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SubjectRe: Remote fork() and Parallel Programming
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Date
ralf@uni-koblenz.de writes:

> On Fri, Jun 12, 1998 at 10:21:52PM +0200, Lars Marowsky-Brée wrote:
>
> > On 1998-06-12T11:12:24,
> > Larry McVoy <lm@bitmover.com> said:
> >
> > > : a process, you have to snapshot all related processes and the state of
> > > : the kernel. It's a much better idea to have general persistency and take
> > > : periodic system-wide snapshots.
> > >
> > > Yup. But throw a cluster into the mix and think about saving the state
> > > of all those sockets. It's doable, just a pain in the butt.
> >
> > I am dreaming of doing an "atomic" cp /proc/pid/<> newhost:/proc/ *g*
> >
> > Seriously: Shouldn't be all information relating to a process and it's
> > resource reside in /proc? This might be the first step to get process
> > migration going, since then you could implement a clean interface.
> >
> > (You can implement this using other tricks, but using the proc fs has a
> > certain "clean" and consistent appeal to me)
>
> It seems a lot of people hasn't understood that moving a process is
> *far* more than just it's resources. It's less the silver bullet that
> many people dream of than more the dragon hiding between the cluster's
> back.
>
> Think of issues like a filepointer for a file which has grown since the
> process snapshot was taken / started to be moved. Assume it was pointing
> to the last byte and the file has grown. So now, where to position the
> file when relaunching the process?

I think that's a bad example, because even non-migrating processes have
to handle this case (because Linux is multi-process) and in Linux
O_APPEND is handled in the low level filesystem atomically anyways.

If they don't want the file modified under them they should use flock().




-Andi

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