Re: [PATCH 05/10] Core checkpoint/restart support code
From: Matt Helsley
Date: Mon Apr 04 2011 - 18:36:45 EST
On Mon, Apr 04, 2011 at 04:43:29PM -0500, Nathan Lynch wrote:
> On Mon, 2011-04-04 at 13:32 -0400, Oren Laadan wrote:
> > From the technical point of view it *is* a big problem: there are
> > very good reasons why we chose a certain design.
> > If Natahan is suggesting in-kernel tree creation as a temporary thing
> > to simplify the code for review - then, given that this patch handles
> > a single process, doing so add lots of unnecessary code, all of which
> > in the kernel.
> > If this is the beginning of a permanent approach, then it is totally
> > incompatible with what we have done so far, and severely restricts
> > the kind of use--cases of the project, potentially making it too
> > unattractive for many natural adaptors, like HPC users. Sorry, nack.
> It's not a stopgap measure to "ease review" or whatever; recreating the
> task tree in-kernel is a fundamental - and simplifying - part of the
> design. I have earned through painful experience the opinion that
> recreating the task tree in userspace is pretty much insane, as is
> exposing the pid allocator to userspace via eclone(2), as is attempting
> to support c/r of any resource that isn't isolated/virtualized, as is
> having every recreated task "rendezvous" in the kernel by having them
> all call restart(2), even though little significant work can be done in
So far we've been proceeding under the assumption that some userspace
code ugliness was acceptable if it simplified the kernel code. With
ghost issues and the stuff you've mentioned above I think it's become
questionable whether that choice has simplified the kernel code enough
and trying something different is valuable.
At this point the only advantage I still see in userspace task creation for
restart is the reviewability of it. eclone is a small piece of code that
can be reviewed independently of restart and thus will prove alot easier to
review for correctness and security than in-kernel task creation for restart.
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