linux-kernel - Re: [Ksummit-2010-discuss] checkpoint-restart: naked patch

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Date:	Mon, 8 Nov 2010 11:55:40 -0500
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Oren Laadan <orenl@...columbia.edu>
Cc:	ksummit-2010-discuss@...ts.linux-foundation.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@....de>
Subject: Re: [Ksummit-2010-discuss] checkpoint-restart: naked patch

On Tue, Nov 2, 2010 at 3:30 PM, Oren Laadan <orenl@...columbia.edu> wrote:
> Hi,
>
> Following the discussion yesterday, here is a linux-cr diff that
> that is limited to changes to existing code.
>
> The diff doesn't include the eclone() patches. I also tried to strip
> off the new c/r code (either code in new files, or new code within
> #ifdef CONFIG_CHECKPOINT in existing files).
>
> I left a few such snippets in, e.g. c/r syscalls templates and
> declaration of c/r specific methods in, e.g. file_operations.
>
> The remaining changes in this patch include new freezer state
> ("CHECKPOINTING"), mostly refactoring of exsiting code, and a bit
> of new helpers.
>
> Disclaimer: don't try to compile (or apply) - this is only intended
> to give a ballpark of how the c/r patches change existing code.
[...]
>  159 files changed, 2031 insertions(+), 587 deletions(-)

FWIW...

This patch has far reaching changes which quite frankly scare me;
primarily because c/r changes many long-held assumptions about how
Linux processes work.  It needs to track a large amount of state with
lots of corner cases, and the Linux process model is already quite
complex.  I know this is a fluffy hand-waving critique, but without
being convinced of a strong general-purpose use-case, it is hard to
get excited about a solution that touches large amounts of common
code.

c/r of desktop processes doesn't seem interesting other that as a test
case, but I can possibly be convinced about HPC, embedded, industrial,
or telecom use-cases, but for custom/specific-purpose applications the
question must be asked if a fully user space or joint user/kernel
method would better solve the problem.

You mentioned in a reply that this overview diff includes both
cleanups and required changes.  I suggest posting the cleanup patches
as soon as possible so that this diff becomes simpler.

Also:

> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 9458685..335a4b3 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -93,6 +93,10 @@ config STACKTRACE_SUPPORT
>  config HAVE_LATENCYTOP_SUPPORT
>        def_bool y
>
> +config CHECKPOINT_SUPPORT
> +       bool
> +       default y
> +

Definitely should not default to 'y', and needs to be user-selectable.

g.
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