Process IDs in a multi-namespace world [LWN.net]

Process IDs in a multi-namespace world

Posted Nov 8, 2007 3:44 UTC (Thu) by Gollum (subscriber, #25237)
In reply to: Process IDs in a multi-namespace world by samroberts
Parent article: Process IDs in a multi-namespace world

If the processes are isolated in a container, it makes it possible at some point in the future
to migrate the entire container to different hardware (assuming that other resources like
filesystems are still reachable).

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Process IDs in a multi-namespace world

Posted Nov 8, 2007 23:42 UTC (Thu) by giraffedata (subscriber, #1954) [Link]

If the processes are isolated in a container, it makes it possible at some point in the future to migrate the entire container

The PID problem fades into insignificance compared to the difficulty of migrating all the other state of a container - all the state in the kernel that uses the global kernel address space, such as inodes, plus the state that lives outside Linux, such as TCP connections and SCSI tasks.

I would wait until those problems are solved before complicating the PID namespace in the name of migration.

Process IDs in a multi-namespace world

Posted Nov 11, 2007 22:37 UTC (Sun) by kolyshkin (subscriber, #34342) [Link]

The PID problem fades into insignificance compared to the difficulty of migrating all the other state of a container - all the state in the kernel that uses the global kernel address space, such as inodes, plus the state that lives outside Linux, such as TCP connections and SCSI tasks.
I would wait until those problems are solved before complicating the PID namespace in the name of migration.

I guess you might want to take a look at OpenVZ (and if you want to see the actual kernel code it's under kernel/cpt/ in source tree, for example, here).

And OpenVZ is not the only one available implementation of containers migration in Linux -- two others I know are Meiosys Metacluster and Zap (both are closed-source unfortunately although Zap may become opensource; also they tend to concentrate on migration while OpenVZ sees it as just another feature of containers).