Re: [RFC][patch 00/21] PID Virtualization: Overview and Patches

[Gerrit Huizenga <gh@us.ibm.com>]

On Thu, 15 Dec 2005 09:35:57 EST, Hubertus Franke wrote:
> This patchset is a followup to the posting by Serge.
> http://marc.theaimsgroup.com/?l=linux-kernel&m=113200410620972&w=2
> 
> In this patchset here, we are providing the pid virtualization mentioned
> in serge's posting.
> 
> > I'm part of a project implementing checkpoint/restart processes.
> > After a process or group of processes is checkpointed, killed, and
> > restarted, the changing of pids could confuse them.  There are many
> > other such issues, but we wanted to start with pids.
> >
> > This patchset introduces functions to access task->pid and ->tgid,
> > and updates ->pid accessors to use the functions.  This is in
> > preparation for a subsequent patchset which will separate the kernel
> > and virtualized pidspaces.  This will allow us to virtualize pids
> > from users' pov, so that, for instance, a checkpointed set of
> > processes could be restarted with particular pids.  Even though their
> > kernel pids may already be in use by new processes, the checkpointed
> > processes can be started in a new user pidspace with their old
> > virtual pid.  This also gives vserver a simpler way to fake vserver
> > init processes as pid 1.  Note that this does not change the kernel's
> > internal idea of pids, only what users see.
> >
> > The first 12 patches change all locations which access ->pid and
> > ->tgid to use the inlined functions.  The last patch actually
> > introduces task_pid() and task_tgid(), and renames ->pid and ->tgid
> > to __pid and __tgid to make sure any uncaught users error out.
> >
> > Does something like this, presumably after much working over, seem
> > mergeable?
> 
> These patches build on top of serge's posted patches (if necessary
> we can repost them here).
> 
> PID Virtualization is based on the concept of a container.
> The ultimate goal is to checkpoint/restart containers. 
> 
> The mechanism to start a container 
> is to 'echo "container_name" > /proc/container'  which creates a new
> container and associates the calling process with it. All subsequently
> forked tasks then belong to that container.
> There is a separate pid space associated with each container.
> Only processes/task belonging to the same container "see" each other.
> The exception is an implied default system container that has 
> a global view.
> 
> The following patches accomplish 3 things:
> 1) identify the locations at the user/kernel boundary where pids and 
>    related ids ( pgrp, sessionids, .. ) need to be (de-)virtualized and
>    call appropriate (de-)virtualization functions.
> 2) provide the virtualization implementation in these functions.
> 3) implement a container object and a simple /proc interface to create one
> 4) provide a per container /proc/fs
> 
> -- Hubertus Franke    (frankeh@watson.ibm.com)
> -- Cedric Le Goater   (clg@fr.ibm.com)
> -- Serge E Hallyn     (serue@us.ibm.com)
> -- Dave Hansen        (haveblue@us.ibm.com)

I think this is actually quite interesting in a number of ways - it
might actually be a way of cleanly addressing several current out
of tree problems, several of which are indpendently (occasionally) striving
for mainline adoption:  vserver, openvz, cluster checkpoint/restart.

I think perhaps this could also be the basis for a CKRM "class"
grouping as well.  Rather than maintaining an independent class
affiliation for tasks, why not have a class devolve (evolve?) into
a "container" as described here.  The container provides much of
the same grouping capabilities as a class as far as I can see.  The
right information would be availble for scheduling and IO resource
management.  The memory component of CKRM is perhaps a bit tricky
still, but an overall strategy (can I use that word here? ;-) might
be to use these "containers" as the single intrinsic grouping mechanism
for vserver, openvz, application checkpoint/restart, resource
management, and possibly others?

Opinions, especially from the CKRM folks?  This might even be useful
to the PAGG folks as a grouping mechanism, similar to their jobs or
containers.

"This patchset solves multiple problems".

gerrit
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