Messages in this thread | | | Date | Thu, 9 Oct 2008 15:17:01 +0200 | From | Ingo Molnar <> | Subject | Re: [RFC v6][PATCH 0/9] Kernel based checkpoint/restart |
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* Dave Hansen <dave@linux.vnet.ibm.com> wrote:
> On Thu, 2008-10-09 at 14:46 +0200, Ingo Molnar wrote: > > * Oren Laadan <orenl@cs.columbia.edu> 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:
set_current_nocr();
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 !CONFIG_CHECKPOINT_RESTART case.
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.");
Ingo
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