Re: [PATCH 0/9] OpenVZ kernel based checkpointing/restart

Serge E. Hallyn
2008-09-03T14:20:14Z

Quoting Cedric Le Goater (clg@fr.ibm.com):
> Andrey Mirkin wrote:
> > This patchset introduces kernel based checkpointing/restart as it is
> > implemented in OpenVZ project. This patchset has limited functionality and
> > are able to checkpoint/restart only single process. Recently Oren Laaden
> > sent another kernel based implementation of checkpoint/restart. The main
> > differences between this patchset and Oren's patchset are:
> >
> > * In this patchset checkpointing initiated not from the process
> > (right now we do not have a container, only namespaces), Oren's patchset
> > performs checkpointing from the process context.
> >
> > * Restart in this patchset is initiated from process, which restarts a new
> > process (in new namespaces) with saved state. Oren's patchset uses the same
> > process from which restart was initiated and restore saved state over it.
> >
> > * Checkpoint/restart functionality in this patchset is implemented as a kernel
> > module
>
> why ? Do we really think that C/R implementations will be so different that
> we will need C/R ops to support all of them ? I imagine that there could be
> different models :

At the mini-summit two reasons were brought up to make it a module:

1. So sysadmins worried about security implications can
completely unload the module

2. So developers can unload and reload the module while
testing.

> 1. brute force : dump it all and kill
> 2. incremental
> 3. live migration
> ...

Actually I don't think we expected to use different implementations for
those.

> But I see all of them really tied to the kernel internals.
>
> The first issues I see with this direction are some EXPORT_SYMBOL() that would
> be useless without a module.
>
> > As checkpointing is initiated not from the process which state should be saved
> > we should freeze a process before saving its state. Right now Container Freezer
> > from Matt Helsley can be used for this.
>
> OK that's integrated and Daniel's tools :
>
> http://lxc.cvs.sourceforge.net/lxc/
>
> one more reason to work on integration :)
>
> C.
>
>
> > This patchset introduce only a concept how kernel based checkpointing/restart
> > can be implemented and are able to checkpoint/restart only a single process
> > with simple VMAs.
> >
> > I've tried to split my patchset in small patches to make review more easier.
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> >
>
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