linux-kernel - Re: Checkpoint/restart (was Re: [PATCH 0/4] - v2

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Message-ID: <20080710173246.GA1857@us.ibm.com>
Date:	Thu, 10 Jul 2008 12:32:46 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Oren Laadan <orenl@...columbia.edu>,
	Kirill Korotaev <dev@...allels.com>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, Nadia.Derbey@...l.net,
	Andrew Morton <akpm@...ux-foundation.org>,
	nick@...k-andrew.net, Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: Checkpoint/restart (was Re: [PATCH 0/4] - v2 - Object creation
	with a specified id)

Quoting Dave Hansen (dave@...ux.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
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