Re: [PATCH 1/4] Virtualization/containers: introduction

[Hubertus Franke <frankeh@watson.ibm.com>]

Sam Vilain wrote:
> Hubertus Franke wrote:
> 
>> The container is just an umbrella object that ties every "virtualized" 
>> subsystem together.
> 
> 
> I like this description; it matches roughly with the concepts as
> presented by vserver; there is the process virtualisation (vx_info), and
> the network virtualisation (nx_info) of Eric's that has been integrated
> to the vserver 2.1.x development branch.  However the vx_info has become
> the de facto umbrella object space as well.  These could almost
> certainly be split out without too much pain or incurring major
> rethinks.
> 
> Sam.
> 


Agreed.. here are some issued we learned from other projects that had
similar interception points.

Having a central umbrella object (let's stick to the name container)
is useful, but being the only object through which every access has to
pass may have drawbacks..

task->container->pspace->pidmap[offset].page   implies potential
cachemisses etc.

If overhead becomes too large, then we can stick (cache) the pointer
additionally in the task struct. But ofcourse that should be carefully
examined on a per subsystem base...

==
Another thing to point out is that container's can have overlaps.

C/R should be a policy thing. So if each "subsystem"

>  Quote Eric>>>
> PIDS
> UIDS
> SYSVIPC
> NETWORK
> UTSNAME
> FILESYSTEM

is represented as a NAMESPACE, then one can pick and choose as a
policy how these constitute at a conceptual level as a container.
You want something migratable you better make sure that
container implies unique subsystems.
Maybe you want to nest containers, but only want to create a
separate pidspaces for performance isolation (see planetlab work
with vserver).
So, there are many possibilities, that might make perfect sense
for different desired solutions and it seems with the
clone ( CLONE_FLAGS_NSPACE_[PIDS/UIDS/SYS.../FS] ) one gets a solution
that is flexible, yet embodies may requirements.....

-- Hubertus