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    SubjectRe: [RFC v13][PATCH 00/14] Kernel based checkpoint/restart
    On Thu, 2009-02-12 at 13:30 -0600, Matt Mackall wrote:
    > On Thu, 2009-02-12 at 10:11 -0800, Dave Hansen wrote:
    > > * Filesystem state
    > > * contents of files
    > > * mount tree for individual processes
    > > * flock
    > > * threads and sessions
    > > * CPU and NUMA affinity
    > > * sys_remap_file_pages()
    > I think the real questions is: where are the dragons hiding? Some of
    > these are known to be hard. And some of them are critical checkpointing
    > typical applications. If you have plans or theories for implementing all
    > of the above, then great. But this list doesn't really give any sense of
    > whether we should be scared of what lurks behind those doors.

    This is probably a better question for people like Pavel, Alexey and
    Cedric to answer.

    > Some of these things we probably don't have to care too much about. For
    > instance, contents of files - these can legitimately change for a
    > running process. Open TCP/IP sockets can legitimately get reset as well.
    > But others are a bigger deal.

    Legitimately, yes. But, practically, these are things that we need to
    handle because we want to make any checkpoint/restart as transparent as
    possible. Resetting people's network connections is not exactly illegal
    but not very nice or transparent either.

    > Also, what happens if I checkpoint a process in 2.6.30 and restore it in
    > 2.6.31 which has an expanded idea of what should be restored? Do your
    > file formats handle this sort of forward compatibility or am I
    > restricted to one kernel?

    In general, you're restricted to one kernel. But, people have mentioned
    that, if the formats change, we should be able to write in-userspace
    converters for the checkpoint files.

    -- Dave

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