Containers/Mini-summit 2008

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There was a containers mini-summit at the OLS'08. This page served for organizing this event.

When: 22nd of July 2008, 8:30-16:30
Where: Ottawa, ON, Canada, Novotel Hotel (Albion A).


For the notes from the mini-summit, see Containers/Mini-summit 2008 notes.


The mini-summit proposal sent to OLS organizers; see proposal.

Topics to discuss[edit]

  • Device accessibility cgroup (maybe with remap ability)
  • TTYs
  • Syslog
  • Checkpoint/restart
  • Memory controllers
  • more?..

List of attendees[edit]

Please fill in your name here if you are going to attend, or email kir at openvz dot org if you are too lazy. Surely the list is not final, so put your name even if you are not sure you can make it.

This list is in no particular order.

  1. Pavel Emelyanov
  2. Denis Lunev
  3. Andrey Mirkin
  4. Serge Hallyn
  5. Dave Hansen
  6. Daniel Lezcano
  7. Srivatsa Vaddagiri
  8. Balbir Singh
  9. Sukadev Bhattiprolu
  10. Paul Menage
  11. Eric W. Biederman
  12. Oren Laadan
  13. Yamamoto Takashi
  14. Kamezawa Hiroyuki
  15. Benjamin Thery
  16. Herbert Pötzl
  17. Oleg Nesterov
  18. Dhaval Giani
  19. Bart Trojanowski
  20. Joseph Ruscio
  21. Constant Chan
  22. Linda Knippers
  23. Satoshi Uchida
  24. Masahiko Takahashi
  25. Martine Silbermann
  26. Benoit des Ligneris
  27. Patrick Naubert
  28. Daisuke Nishimura
  29. Sudhir Kumar
  30. Munehiro Ikeda
  31. Kamalesh Babulal
  32. John Schulz
  33. Poornima Nayak
  34. Gyuil Cha
  35. YoungHo Kim
  36. Rob Woolley
  37. Daniel Robbins
  38. Jason Baron
  39. Subrata Modak
  40. Veerendra C
  41. Joe MacDonald
  42. Andrew Theurer
  43. Myron Stowe
  44. Peter Teoh
  45. Ricky Liang


  • Namespaces/Containers (8:30am-11am)
    • sysfs issues (and any /proc issues)
      • uevents/hotplug
    • Network namespaces issues
      • multiple namespaces in one process
    • Device namespace design?
    • User namespace
    • Additional needed namespaces
      • Small namespaces What to do with small subsystem that might need virtualization. E.g. in openvz we have FUSE, binfmt_misc and some other small stuff virtualized. But how to merge it in mainline? Create a separate namespace for each? Mere them into one? How to call this then?
    • Handling filesystem/namespace synchronization (not sure what the issue is)
    • Container design
      • How to enter a container
      • Nature of a 'container' — kernel object or userspace fiction
  • Cgroups+Resource management (11:30-2pm)
    • Cgroup implementation
      • Locking (don't let cgroup_lock() become the BKL)
      • Transactional attachment
      • "procs" file
      • User-space notification API
        • Resource counter hit soft/hard limit
        • Task entered/left cgroup
        • OOM occurred
      • Binary statistics API
    • Existing cgroups
      • Memory (Balbir's NOTE: I would prefer to take some of this discussion to my memory controller BoF on Wednesday. Lets discuss this at the end)
        • Supporting over-commit and guarantees
        • Soft-limits
        • Hierarchical borrowing - in kernel or userspace?
        • Per-cgroup refault information?
      • Kernel memory
      • Device
      • Memrlimit
        • Some push-back over this - can we give real use cases?
      • CPU scheduler
    • Additional cgroups and their design
      • Swap (separate subsystem or merge with memory?)
      • Disk I/O (several proposed designs)
      • Network traffic classification
      • Freezer
      • Signaller
      • OOM Handler
    • libcg - userspace explotation of control groups/resource management
      • Overview so far
      • Is kernel-based reclassification needed?
      • Real use-cases
      • Future directions

  • Checkpoint/Restart (2:30pm-5pm)
    • Documentation : Look at "See Also" section below
    • Goals and expectations of this summit
      • identify, discuss and (if possible) agree on the general design
      • identify, discuss and (if possible) agree on the technical points
      • decide on priorities for different components (eg. high, medium, low) such that the final outcome is a practical road-map that would keep us busy for (at least) until the next OLS (though the "O" may change ;)
    • What are the problems that the linux community can solve with the checkpoint/restart ?
    • Preparing the kernel internals
      • How we implement it without affecting long term maintainability ?
      • What are the kernel subsystems, process resources and framework for CR ?
      • Which pieces to target first ?

The following technical points can be discussed during the mini-summit if we have time or later at the OLS.

    • Checkpointing / Restarting
      • Reaching a quescient point - network, processes, aio, avoiding side effects of quiesce/revive
      • Checkpoint - signal handler ? syscall ? crfs ? process hierarchy, resource dependencies, system and process resources
      • Restarting - New binary format handler ? converting between formats (from older kernel to newer)
      • Notification to processes which explicitly wish to be notified about quiesce, checkpoint and restart - container state ? new signals ?
    • Determining the userspace API - Posix 1003.1m ?
    • Passing the kernel internal state to/from userspace - coredump like file ? swap per container ? netlinks, CR filesystem ? army of different call for the CR (proc, existing syscalls, ...)
    • Hopefully we can continue to discuss in the next days and get a bit of a hackfest going during OLS :)


  • Namespaces/containers: Serge Hallyn, Dave Hansen
  • Cgroups and resource management: Paul Menage, Balbir Singh, Dhaval Giani
  • Checkpoint/restart: Daniel Lezcano, Oren Laadan

See also[edit]