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

    Andrey Mirkin wrote:
    > On Monday 20 October 2008 19:55 Dave Hansen wrote:
    >> On Mon, 2008-10-20 at 16:14 +0400, Andrey Mirkin wrote:
    >>> Right now my patchset (v2) provides an ability to checkpoint and restart
    >>> a group of processes. The process of checkpointing and restart can be
    >>> initiated from external process (not from the process which should be
    >>> checkpointed).
    >> Absolutely. Oren's code does it this way to make for a smaller patch at
    >> first. The syscall takes a pid argument so it is surely expected to be
    >> expanded upon later.
    >>> Also I think that all the restart job (including process forking) should
    >>> be done in kernel, as in this case we will not depend on user space and
    >>> will be more secure. This is also implemented in my patchset.
    >> Do you think that this is an approach that Oren's patches are married
    >> to, or is this a "feature" we can add on later?
    > Well, AFAICS from Oren's patch set his approach is oriented on process
    > creation in user space. I think we should choose right now what approach will
    > be used for process creation.

    This is inaccurate.

    I intentionally did not address how processes will be created, by
    simply allowing either way to be added to the patch.

    I do agree that we probably want to decide how to do it. However,
    there is also room to allow for both approaches, in a compatible
    way, should we wish to explore both.

    > We have two options here: fork processes in kernel or fork them in user space.
    > If process will be forked in user space, then there will be a gap when process
    > will be in user space and can be killed with received signal before entering

    Why do we care about it ?
    Why is there a difference if it is killed before or after entering
    the kernel (e.g. user aborted restart, or kernel OOM kicked in) ?

    > kernel. Also we will need a functionolity to create processes with predefined
    > PID. I think it is not very good to provide such ability to user space. That
    > is why we prefer in OpenVZ to do all the job in kernel.

    This is the weak side of creating the processes in user space -
    that we need such an interface. Note, however, that we can
    easily "hide" it inside the interface of the sys_restart() call,
    and restrict how it may be used.


    >> I don't care which patch set we end up sticking in the kernel. I'm
    >> trying to figure out which code we can more easily build upon in the
    >> future. The fact that Oren's or yours can't do certain little things
    >> right now does not bother me.
    >> Honestly, I'm a little more confident that everyone can work with Oren
    >> since he managed to get 7 revisions of his patch out and make some
    >> pretty large changes while in the same time the OpenVZ patch was only
    >> released twice. I'm not sure what has changed in the OpenVZ patch
    >> between releases, either.
    > That is my fault. I am working right now on my Ph.D, that is why my activity
    > is not very high. But now I hope I will have more time for that.
    >> Are there any reasons that you absolutely can not use the code Oren
    >> posted? Will it not fulfill your needs somehow? If so, could you
    >> please elaborate on how?
    > We have one major difference with Oren's code - how processes are created
    > during restr.
    > Right now I'm trying to port kernel process creation on top of Oren's patches.
    > I agree that working in collaboration will speed up merging of checkpointing
    > to mainstream.
    > Andrey
    > P.S.: Sorry for late reply, my mailer attached your e-mail to wrong thread.
    > _______________________________________________
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