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    SubjectRe: [RFC][PATCH 1/2] Track in-kernel when we expect checkpoint/restart to work
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    On Fri, 2008-10-10 at 11:17 -0400, Oren Laadan wrote:
    >
    > Ingo Molnar wrote:
    > > * Daniel Lezcano <dlezcano@fr.ibm.com> wrote:
    > >
    > >>> By the way, why don't you introduce the reverse operation ?
    > >> I think implementing the reverse operation will be a nightmare, IMHO
    > >> it is safe to say we deny checkpointing for the process life-cycle
    > >> either if the created resource was destroyed before we initiate the
    > >> checkpoint.
    > >
    > > it's also a not too interesting case. The end goal is to just be able to
    > > checkpoint everything that matters - in the long run there simply wont
    > > be many places that are marked 'cannot checkpoint'.
    > >
    > > So the ability to deny a checkpoint is a transitional feature - a
    > > flexible CR todo list in essence - but also needed for
    > > applications/users that want to rely on CR being a dependable facility.
    > >
    > > It would be bad for most of the practical usecases of checkpointing to
    > > allow the checkpointing of an app, just to see it break on restore due
    > > to lost context.
    >
    > Actually it need not wait for restore to fail - it can fail during the
    > checkpoint, as soon as the unsupported feature is encountered.
    >

    Of course, bad things must be spotted at checkpoint time ! :)

    > Adding that flag of what you suggest will help make it more vocal and
    > obvious that a feature isn't supported, even without the user actually
    > trying to take a checkpoint. I like that I idea.
    >

    This flag is weak... testing it gives absolutly no hint whether the
    checkpoint may succeed or not. As it is designed now, a user can only be
    aware that checkpoint is *forever* denied. I agree that it's only useful
    as a "flexible CR todo list".

    In the long run, if there are still things that can prevent checkpoint
    from being consistent, they will have to be checked at checkpoint time.

    Greg.




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