cgroup: fix and update documentation
Misc fixes and updates, make the doc consistent with current cgroup
implementation.
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/cgroups.txt b/Documentation/cgroups.txt
index 42d7c4c..31d12e2 100644
--- a/Documentation/cgroups.txt
+++ b/Documentation/cgroups.txt
@@ -28,7 +28,7 @@
4. Questions
1. Control Groups
-==========
+=================
1.1 What are cgroups ?
----------------------
@@ -143,10 +143,10 @@
Also lets say that the administrator would like to give enhanced network
access temporarily to a student's browser (since it is night and the user
-wants to do online gaming :) OR give one of the students simulation
+wants to do online gaming :)) OR give one of the students simulation
apps enhanced CPU power,
-With ability to write pids directly to resource classes, its just a
+With ability to write pids directly to resource classes, it's just a
matter of :
# echo pid > /mnt/network/<new_class>/tasks
@@ -227,10 +227,13 @@
containing the following files describing that cgroup:
- tasks: list of tasks (by pid) attached to that cgroup
- - notify_on_release flag: run /sbin/cgroup_release_agent on exit?
+ - releasable flag: cgroup currently removeable?
+ - notify_on_release flag: run the release agent on exit?
+ - release_agent: the path to use for release notifications (this file
+ exists in the top cgroup only)
Other subsystems such as cpusets may add additional files in each
-cgroup dir
+cgroup dir.
New cgroups are created using the mkdir system call or shell
command. The properties of a cgroup, such as its flags, are
@@ -257,7 +260,7 @@
To allow access from a cgroup to the css_sets (and hence tasks)
that comprise it, a set of cg_cgroup_link objects form a lattice;
each cg_cgroup_link is linked into a list of cg_cgroup_links for
-a single cgroup on its cont_link_list field, and a list of
+a single cgroup on its cgrp_link_list field, and a list of
cg_cgroup_links for a single css_set on its cg_link_list.
Thus the set of tasks in a cgroup can be listed by iterating over
@@ -271,9 +274,6 @@
1.4 What does notify_on_release do ?
------------------------------------
-*** notify_on_release is disabled in the current patch set. It will be
-*** reactivated in a future patch in a less-intrusive manner
-
If the notify_on_release flag is enabled (1) in a cgroup, then
whenever the last task in the cgroup leaves (exits or attaches to
some other cgroup) and the last child cgroup of that cgroup
@@ -360,8 +360,8 @@
In this directory you can find several files:
# ls
-notify_on_release release_agent tasks
-(plus whatever files are added by the attached subsystems)
+notify_on_release releasable tasks
+(plus whatever files added by the attached subsystems)
Now attach your shell to this cgroup:
# /bin/echo $$ > tasks
@@ -404,19 +404,13 @@
Other fields in the cgroup_subsys object include:
- subsys_id: a unique array index for the subsystem, indicating which
- entry in cgroup->subsys[] this subsystem should be
- managing. Initialized by cgroup_register_subsys(); prior to this
- it should be initialized to -1
+ entry in cgroup->subsys[] this subsystem should be managing.
-- hierarchy: an index indicating which hierarchy, if any, this
- subsystem is currently attached to. If this is -1, then the
- subsystem is not attached to any hierarchy, and all tasks should be
- considered to be members of the subsystem's top_cgroup. It should
- be initialized to -1.
+- name: should be initialized to a unique subsystem name. Should be
+ no longer than MAX_CGROUP_TYPE_NAMELEN.
-- name: should be initialized to a unique subsystem name prior to
- calling cgroup_register_subsystem. Should be no longer than
- MAX_CGROUP_TYPE_NAMELEN
+- early_init: indicate if the subsystem needs early initialization
+ at system boot.
Each cgroup object created by the system has an array of pointers,
indexed by subsystem id; this pointer is entirely managed by the
@@ -434,8 +428,6 @@
See kernel/cgroup.c for more details.
Subsystems can take/release the cgroup_mutex via the functions
-cgroup_lock()/cgroup_unlock(), and can
-take/release the callback_mutex via the functions
cgroup_lock()/cgroup_unlock().
Accessing a task's cgroup pointer may be done in the following ways:
@@ -444,7 +436,7 @@
- inside an rcu_read_lock() section via rcu_dereference()
3.3 Subsystem API
---------------------------
+-----------------
Each subsystem should:
@@ -455,7 +447,8 @@
methods are create/destroy. Any others that are null are presumed to
be successful no-ops.
-struct cgroup_subsys_state *create(struct cgroup *cont)
+struct cgroup_subsys_state *create(struct cgroup_subsys *ss,
+ struct cgroup *cgrp)
(cgroup_mutex held by caller)
Called to create a subsystem state object for a cgroup. The
@@ -470,7 +463,7 @@
it's the root of the hierarchy) and may be an appropriate place for
initialization code.
-void destroy(struct cgroup *cont)
+void destroy(struct cgroup_subsys *ss, struct cgroup *cgrp)
(cgroup_mutex held by caller)
The cgroup system is about to destroy the passed cgroup; the subsystem
@@ -481,7 +474,14 @@
newly-created cgroup if an error occurs after this subsystem's
create() method has been called for the new cgroup).
-int can_attach(struct cgroup_subsys *ss, struct cgroup *cont,
+void pre_destroy(struct cgroup_subsys *ss, struct cgroup *cgrp);
+(cgroup_mutex held by caller)
+
+Called before checking the reference count on each subsystem. This may
+be useful for subsystems which have some extra references even if
+there are not tasks in the cgroup.
+
+int can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
struct task_struct *task)
(cgroup_mutex held by caller)
@@ -492,8 +492,8 @@
called on a fork. If this method returns 0 (success) then this should
remain valid while the caller holds cgroup_mutex.
-void attach(struct cgroup_subsys *ss, struct cgroup *cont,
- struct cgroup *old_cont, struct task_struct *task)
+void attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
+ struct cgroup *old_cgrp, struct task_struct *task)
Called after the task has been attached to the cgroup, to allow any
post-attachment activity that requires memory allocations or blocking.
@@ -505,9 +505,9 @@
void exit(struct cgroup_subsys *ss, struct task_struct *task)
-Called during task exit
+Called during task exit.
-int populate(struct cgroup_subsys *ss, struct cgroup *cont)
+int populate(struct cgroup_subsys *ss, struct cgroup *cgrp)
Called after creation of a cgroup to allow a subsystem to populate
the cgroup directory with file entries. The subsystem should make
@@ -516,7 +516,7 @@
method can return an error code, the error code is currently not
always handled well.
-void post_clone(struct cgroup_subsys *ss, struct cgroup *cont)
+void post_clone(struct cgroup_subsys *ss, struct cgroup *cgrp)
Called at the end of cgroup_clone() to do any paramater
initialization which might be required before a task could attach. For