Re: Checkpoint/restart (was Re: [PATCH 0/4] - v2 - Object creation with a specified id)

["Serge E. Hallyn" <serue@us.ibm.com>]

Quoting Dave Hansen (dave@linux.vnet.ibm.com):
> On Wed, 2008-07-09 at 18:58 -0700, Eric W. Biederman wrote:
> > In the worst case today we can restore a checkpoint by replaying all of
> > the user space actions that took us to get there.  That is a tedious
> > and slow approach.
> 
> Yes, tedious and slow, *and* minimally invasive in the kernel.  Once we
> have a tedious and slow process, we'll have some really good points when
> we try to push the next set of patches to make it less slow and tedious.
> We'll be able to describe an _actual_ set of problems to our fellow
> kernel hackers.
> 
> So, the checkpoint-as-a-corefile idea sounds good to me, but it
> definitely leaves a lot of questions about exactly how we'll need to do
> the restore.

Talking with Dave over irc, I kind of liked the idea of creating a new
fs/binfmt_cr.c that executes a checkpoint-as-a-coredump file.

One thing I do not like about the checkpoint-as-coredump is that it begs
us to dump all memory out into the file.  Our plan/hope was to save
ourselves from writing out most memory by:

	1. associating a separate swapfile with each container
	2. doing a swapfile snapshot at each checkpoint
	3. dumping the pte entries (/proc/self/)

If we do checkpoint-as-a-coredump, then we need userspace to coordinate
a kernel-generated coredump with a user-generated (?) swapfile snapshot.
But I guess we figure that out later.

-serge