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

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Date:	Thu, 10 Jul 2008 11:55:34 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	Dave Hansen <dave@...ux.vnet.ibm.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)

"Serge E. Hallyn" <serue@...ibm.com> writes:

>> 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.

Well it is a matter of which VMAs you dump.  For things that are file backed
you need to dump them.

I don't know that even a binfmt for per process level checkpoints is sufficient
but I do know having something of that granularity looks much easier.  Otherwise
it takes a bazillian little syscalls to do things no one else is interested in doing.

Eric
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