[Devel] [patch00/05]: Containers(V2)- Introduction

[Rohit Seth]

Containers:

Commodity HW is becoming more powerful.  This is giving opportunity to
run different workloads on the same platform for better HW resource
utilization.  To run different workloads efficiently on the same
platform, it is critical that we have a notion of limits for each
workload in Linux kernel.  Current cpuset feature in Linux kernel
provides grouping of CPU and memory support to some extent (for NUMA
machines).  

For example, a user can run a batch job like backup inside containers.
This job if run unconstrained could step over most of the memory present
in system thus impacting other workloads running on the system at that
time.  But when the same job is run inside containers then the backup
job is run within container limits.

We use the term container to indicate a structure against which we track
and charge utilization of system resources like memory, tasks etc for a
workload. Containers will allow system admins to customize the
underlying platform for different applications based on their
performance and HW resource utilization needs.  Containers contain
enough infrastructure to allow optimal resource utilization without
bogging down rest of the kernel.  A system admin should be able to
create, manage and free containers easily.

At the same time, changes in kernel are minimized so as this support can
be easily integrated with mainline kernel.

The user interface for containers is through configfs.  Appropriate file
system privileges are required to do operations on each container.
Currently implemented container resources are automatically visible to
user space through /configfs/container/<container_name> after a
container is created.

Signed-off-by: Rohit Seth <rohitseth at google.com>

Diffstat for the patch set (against linux-2.6.18-rc6-mm2_:

 Documentation/containers.txt |   65 ++++
 fs/inode.c                   |    3
 include/linux/container.h    |  167 ++++++++++
 include/linux/fs.h           |    5
 include/linux/mm_inline.h    |    4
 include/linux/mm_types.h     |    4
 include/linux/sched.h        |    6
 init/Kconfig                 |    8
 kernel/Makefile              |    1
 kernel/container_configfs.c  |  440 ++++++++++++++++++++++++++++
 kernel/exit.c                |    2
 kernel/fork.c                |    9
 mm/Makefile                  |    2
 mm/container.c               |  658 +++++++++++++++++++++++++++++++++++++++++++
 mm/container_mm.c            |  512 +++++++++++++++++++++++++++++++++
 mm/filemap.c                 |    4
 mm/page_alloc.c              |    3
 mm/rmap.c                    |    8
 mm/swap.c                    |    1
 mm/vmscan.c                  |    1
 20 files changed, 1902 insertions(+), 1 deletion(-)

Changes from version 1:
Fixed the Documentation error
Fixed the corruption in container task list
Added the support for showing all the tasks belonging to a container
through showtask attribute
moved the Kconfig changes to init directory (from mm)
Fixed the bug of unregistering container subsystem if we are not able to
create workqueue
Better support for handling limits for file pages.  This now includes
support for flushing and invalidating page cache pages.
Minor other changes.

*****************************************************************
This patch set has basic container support that includes:

- Create a container using mkdir command in configfs

- Free a container using rmdir command

- Dynamically adjust memory and task limits for container.

- Add/Remove a task to container (given a pid)

- Files are currently added as part of open from a task that already
belongs to a container.

- Keep track of active, anonymous, mapped and pagecache usage of
container memory

- Does not allow more than task_limit number of tasks to be created in
the container.

- Over the limit memory handler is called when number of pages (anon +
pagecache) exceed the limit.  It is also called when number of active
pages exceed the page limit.  Currently, this memory handler scans the
mappings and tasks belonging to container (file and anonymous) and tries
to deactivate pages.  If the number of page cache pages is also high
then it also invalidate mappings.  The thought behind this scheme is, it
is okay for containers to go over limit as long they run in degraded
manner when they are over their limit. Also, if there is any memory
pressure then pages belonging to over the limit container(s) become
prime candidates for kernel reclaimer.  Container mutex is also held
during the time this handler is working its way through to prevent any
further addition of resources (like tasks or mappings) to this
container.  Though it also blocks removal of same resources from the
container for the same time. It is possible that over the limit page
handler takes lot of time if memory pressure on a container is
continuously very high.  The limits, like how long a task should
schedule out when it hits memory limit, is also on the lower side at
present (particularly when it is memory hogger).  But should be easy to
change if need be.

- Indicate the number of times the page limit and task limit is hit

- Indicate the tasks (pids) belonging to container.

Below is a one line description for patches that will follow:

[patch01]: Documentation on how to use containers
(Documentation/container.txt)

[patch02]: Changes in the generic part of kernel code

[patch03]: Container's interface with configfs

[patch04]: Core container support

[patch05]: Over the limit memory handler.

TODO: 

- some code(like container_add_task) in mm/container.c should go
elsewhere.
- Support adding/removing a file name to container through configfs
- /proc/pid/container to show the container id (or name)
- More testing for memory controller.  Currently it is possible that
limits are exceeded.  See if a call to reclaim can be easily integrated.
- Kernel memory tracking (based on patches from BC)
- Limit on user locked memory
- Huge memory support
- Stress testing with containers
- One shot view of all containers
- CKRM folks are interested in seeing all processes belonging to a
container.  Add the attribute show_tasks to container.
- Add logic so that the sum of limits are not exceeding appropriate
system requirements.
- Extend it with other controllers (CPU and Disk I/O)
- Add flags bits for supporting different actions (like in some cases
provide a hard memory limit and in some cases it could be soft).
- Capability to kill processes for the extreme cases.
 ...

This is based on lot of discussions over last month or so.  I hope this
patch set is something that we can agree and more support can be added
on top of this.  Please provide feedback and add other extensions that
are useful in the TODO list.

Thanks,
-rohit




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