Commit 6abc8ca1 authored by Tejun Heo's avatar Tejun Heo

cgroup: define controller file conventions

Traditionally, each cgroup controller implemented whatever interface
it wanted leading to interfaces which are widely inconsistent.
Examining the requirements of the controllers readily yield that there
are only a few control schemes shared among all.

Two major controllers already had to implement new interface for the
unified hierarchy due to significant structural changes.  Let's take
the chance to establish common conventions throughout all controllers.

This patch defines CGROUP_WEIGHT_MIN/DFL/MAX to be used on all weight
based control knobs and documents the conventions that controllers
should follow on the unified hierarchy.  Except for io.weight knob,
all existing unified hierarchy knobs are already compliant.  A
follow-up patch will update io.weight.

v2: Added descriptions of min, low and high knobs.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Peter Zijlstra <peterz@infradead.org>
parent d770e558
...@@ -23,10 +23,13 @@ CONTENTS ...@@ -23,10 +23,13 @@ CONTENTS
5. Other Changes 5. Other Changes
5-1. [Un]populated Notification 5-1. [Un]populated Notification
5-2. Other Core Changes 5-2. Other Core Changes
5-3. Per-Controller Changes 5-3. Controller File Conventions
5-3-1. blkio 5-3-1. Format
5-3-2. cpuset 5-3-2. Control Knobs
5-3-3. memory 5-4. Per-Controller Changes
5-4-1. blkio
5-4-2. cpuset
5-4-3. memory
6. Planned Changes 6. Planned Changes
6-1. CAP for resource control 6-1. CAP for resource control
...@@ -372,14 +375,75 @@ supported and the interface files "release_agent" and ...@@ -372,14 +375,75 @@ supported and the interface files "release_agent" and
- The "cgroup.clone_children" file is removed. - 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. - 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 - 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. of the nearest non-empty ancestor, instead of being moved to it.
...@@ -388,7 +452,7 @@ supported and the interface files "release_agent" and ...@@ -388,7 +452,7 @@ supported and the interface files "release_agent" and
masks of the nearest non-empty ancestor. 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 - use_hierarchy is on by default and the cgroup file for the flag is
not created. not created.
......
...@@ -22,6 +22,15 @@ ...@@ -22,6 +22,15 @@
#ifdef CONFIG_CGROUPS #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 */ /* a css_task_iter should be treated as an opaque object */
struct css_task_iter { struct css_task_iter {
struct cgroup_subsys *ss; struct cgroup_subsys *ss;
......
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