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SubjectRe: [RFC v6][PATCH 0/9] Kernel based checkpoint/restart

* Dave Hansen <> wrote:

> On Thu, 2008-10-09 at 14:46 +0200, Ingo Molnar wrote:
> > * Oren Laadan <> wrote:
> >
> > > These patches implement basic checkpoint-restart [CR]. This version
> > > (v6) supports basic tasks with simple private memory, and open files
> > > (regular files and directories only). Changes mainly cleanups. See
> > > original announcements below.
> >
> > i'm wondering about the following productization aspect: it would be
> > very useful to applications and users if they knew whether it is safe to
> > checkpoint a given app. I.e. whether that app has any state that cannot
> > be stored/restored yet.
> Absolutely!
> My first inclination was to do this at checkpoint time: detect and
> tell users why an app or container can't actually be checkpointed.
> But, if I get you right, you're talking about something that happens
> more during the runtime of the app than during the checkpoint. This
> sounds like a wonderful approach to me, and much better than what I
> was thinking of.
> What kind of mechanism do you have in mind?
> int sys_remap_file_pages(...)
> {
> ...
> oh_crap_we_dont_support_this_yet(current);
> }
> Then the oh_crap..() function sets a task flag or something?

yeah, something like that. A key aspect of it is that is has to be very
low-key on the source code level - we dont want to sprinkle the kernel
with anything ugly. Perhaps something pretty explicit:

current->flags |= PF_NOCR;
as we do the same thing today for certain facilities:

current->flags |= PF_NOFREEZE;
you probably want to hide it behind:


and have a set_task_nocr() as well, in case there's some proxy state
installed by another task.

Via such wrappers there's no overhead at all in the

Plus you could drive the debug mechanism via it as well, by using a
trivial extension of the facility:

set_current_nocr("CR: sys_remap_file_pages not supported yet.");
set_task_nocr(t, "CR: PI futexes not supported yet.");


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