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

[ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman)]

"Serge E. Hallyn" <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> 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