cgroup: define controller file conventions

5. Other Changes

  5-1. [Un]populated Notification

  5-2. Other Core Changes

  5-3. Per-Controller Changes

    5-3-1. blkio

    5-3-2. cpuset

    5-3-3. memory

  5-3. Controller File Conventions

    5-3-1. Format

    5-3-2. Control Knobs

  5-4. Per-Controller Changes

    5-4-1. blkio

    5-4-2. cpuset

    5-4-3. memory

6. Planned Changes

  6-1. CAP for resource control

- The "cgroup.clone_children" file is removed.

5-3. Per-Controller Changes

5-3. Controller File Conventions

5-3-1. blkio

5-3-1. Format

In general, all controller files should be in one of the following

formats whenever possible.

- Values only files

  VAL0 VAL1...\n

- Flat keyed files

  KEY0 VAL0\n

  KEY1 VAL1\n

  ...

- Nested keyed files

  KEY0 SUB_KEY0=VAL00 SUB_KEY1=VAL01...

  KEY1 SUB_KEY0=VAL10 SUB_KEY1=VAL11...

  ...

For a writeable file, the format for writing should generally match

reading; however, controllers may allow omitting later fields or

implement restricted shortcuts for most common use cases.

For both flat and nested keyed files, only the values for a single key

can be written at a time.  For nested keyed files, the sub key pairs

may be specified in any order and not all pairs have to be specified.

5-3-2. Control Knobs

- Settings for a single feature should generally be implemented in a

  single file.

- In general, the root cgroup should be exempt from resource control

  and thus shouldn't have resource control knobs.

- If a controller implements ratio based resource distribution, the

  control knob should be named "weight" and have the range [1, 10000]

  and 100 should be the default value.  The values are chosen to allow

  enough and symmetric bias in both directions while keeping it

  intuitive (the default is 100%).

- If a controller implements an absolute resource guarantee and/or

  limit, the control knobs should be named "min" and "max"

  respectively.  If a controller implements best effort resource

  gurantee and/or limit, the control knobs should be named "low" and

  "high" respectively.

  In the above four control files, the special token "max" should be

  used to represent upward infinity for both reading and writing.

- If a setting has configurable default value and specific overrides,

  the default settings should be keyed with "default" and appear as

  the first entry in the file.  Specific entries can use "default" as

  its value to indicate inheritance of the default value.

5-4. Per-Controller Changes

5-4-1. blkio

- blk-throttle becomes properly hierarchical.

5-3-2. cpuset

5-4-2. cpuset

- Tasks are kept in empty cpusets after hotplug and take on the masks

  of the nearest non-empty ancestor, instead of being moved to it.

  masks of the nearest non-empty ancestor.

5-3-3. memory

5-4-3. memory

- use_hierarchy is on by default and the cgroup file for the flag is

  not created.

#ifdef CONFIG_CGROUPS

/*

 * All weight knobs on the default hierarhcy should use the following min,

 * default and max values.  The default value is the logarithmic center of

 * MIN and MAX and allows 100x to be expressed in both directions.

 */

#define CGROUP_WEIGHT_MIN		1

#define CGROUP_WEIGHT_DFL		100

#define CGROUP_WEIGHT_MAX		10000

/* a css_task_iter should be treated as an opaque object */

struct css_task_iter {

	struct cgroup_subsys		*ss;