CGROUPS
-------
-Written by Paul Menage <menage@google.com> based on Documentation/cpusets.txt
+Written by Paul Menage <menage@google.com> based on
+Documentation/cgroups/cpusets.txt
Original copyright statements from cpusets.txt:
Portions Copyright (C) 2004 BULL SA.
2. Usage Examples and Syntax
2.1 Basic Usage
2.2 Attaching processes
+ 2.3 Mounting hierarchies by name
+ 2.4 Notification API
3. Kernel API
3.1 Overview
3.2 Synchronization
state attached to each cgroup in the hierarchy. Each hierarchy has
an instance of the cgroup virtual filesystem associated with it.
-At any one time there may be multiple active hierachies of task
+At any one time there may be multiple active hierarchies of task
cgroups. Each hierarchy is a partition of all tasks in the system.
User level code may create and destroy cgroups by name in an
tracking. The intention is that other subsystems hook into the generic
cgroup support to provide new attributes for cgroups, such as
accounting/limiting the resources which processes in a cgroup can
-access. For example, cpusets (see Documentation/cpusets.txt) allows
+access. For example, cpusets (see Documentation/cgroups/cpusets.txt) allows
you to associate a set of CPUs and a set of memory nodes with the
tasks in each cgroup.
/ \
Prof (15%) students (5%)
-Browsers like firefox/lynx go into the WWW network class, while (k)nfsd go
+Browsers like Firefox/Lynx go into the WWW network class, while (k)nfsd go
into NFS network class.
-At the same time firefox/lynx will share an appropriate CPU/Memory class
+At the same time Firefox/Lynx will share an appropriate CPU/Memory class
depending on who launched it (prof/student).
With the ability to classify tasks differently for different resources
Each cgroup is represented by a directory in the cgroup file system
containing the following files describing that cgroup:
- - tasks: list of tasks (by pid) attached to that cgroup
+ - tasks: list of tasks (by pid) attached to that cgroup. This list
+ is not guaranteed to be sorted. Writing a thread id into this file
+ moves the thread into this cgroup.
+ - cgroup.procs: list of tgids in the cgroup. This list is not
+ guaranteed to be sorted or free of duplicate tgids, and userspace
+ should sort/uniquify the list if this property is required.
+ This is a read-only file, for now.
- 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)
When a task is moved from one cgroup to another, it gets a new
css_set pointer - if there's an already existing css_set with the
desired collection of cgroups then that group is reused, else a new
-css_set is allocated. Note that the current implementation uses a
-linear search to locate an appropriate existing css_set, so isn't
-very efficient. A future version will use a hash table for better
-performance.
+css_set is allocated. The appropriate existing css_set is located by
+looking into a hash table.
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;
Creating, modifying, using the cgroups can be done through the cgroup
virtual filesystem.
-To mount a cgroup hierarchy will all available subsystems, type:
+To mount a cgroup hierarchy with all available subsystems, type:
# mount -t cgroup xxx /dev/cgroup
The "xxx" is not interpreted by the cgroup code, but will appear in
/proc/mounts so may be any useful identifying string that you like.
-To mount a cgroup hierarchy with just the cpuset and numtasks
+To mount a cgroup hierarchy with just the cpuset and memory
subsystems, type:
-# mount -t cgroup -o cpuset,numtasks hier1 /dev/cgroup
+# mount -t cgroup -o cpuset,memory hier1 /dev/cgroup
To change the set of subsystems bound to a mounted hierarchy, just
remount with different options:
+# mount -o remount,cpuset,ns hier1 /dev/cgroup
-# mount -o remount,cpuset,ns /dev/cgroup
+Now memory is removed from the hierarchy and ns is added.
+
+Note this will add ns to the hierarchy but won't remove memory or
+cpuset, because the new options are appended to the old ones:
+# mount -o remount,ns /dev/cgroup
+
+To Specify a hierarchy's release_agent:
+# mount -t cgroup -o cpuset,release_agent="/sbin/cpuset_release_agent" \
+ xxx /dev/cgroup
+
+Note that specifying 'release_agent' more than once will return failure.
Note that changing the set of subsystems is currently only supported
when the hierarchy consists of a single (root) cgroup. Supporting
tree of the cgroups in the system. For instance, /dev/cgroup
is the cgroup that holds the whole system.
+If you want to change the value of release_agent:
+# echo "/sbin/new_release_agent" > /dev/cgroup/release_agent
+
+It can also be changed via remount.
+
If you want to create a new cgroup under /dev/cgroup:
# cd /dev/cgroup
# mkdir my_cgroup
In this directory you can find several files:
# ls
-notify_on_release tasks
+cgroup.procs notify_on_release tasks
(plus whatever files added by the attached subsystems)
Now attach your shell to this cgroup:
# echo 0 > tasks
+2.3 Mounting hierarchies by name
+--------------------------------
+
+Passing the name=<x> option when mounting a cgroups hierarchy
+associates the given name with the hierarchy. This can be used when
+mounting a pre-existing hierarchy, in order to refer to it by name
+rather than by its set of active subsystems. Each hierarchy is either
+nameless, or has a unique name.
+
+The name should match [\w.-]+
+
+When passing a name=<x> option for a new hierarchy, you need to
+specify subsystems manually; the legacy behaviour of mounting all
+subsystems when none are explicitly specified is not supported when
+you give a subsystem a name.
+
+The name of the subsystem appears as part of the hierarchy description
+in /proc/mounts and /proc/<pid>/cgroups.
+
+2.4 Notification API
+--------------------
+
+There is mechanism which allows to get notifications about changing
+status of a cgroup.
+
+To register new notification handler you need:
+ - create a file descriptor for event notification using eventfd(2);
+ - open a control file to be monitored (e.g. memory.usage_in_bytes);
+ - write "<event_fd> <control_fd> <args>" to cgroup.event_control.
+ Interpretation of args is defined by control file implementation;
+
+eventfd will be woken up by control file implementation or when the
+cgroup is removed.
+
+To unregister notification handler just close eventfd.
+
+NOTE: Support of notifications should be implemented for the control
+file. See documentation for the subsystem.
+
3. Kernel API
=============
- add an entry in linux/cgroup_subsys.h
- define a cgroup_subsys object called <name>_subsys
+If a subsystem can be compiled as a module, it should also have in its
+module initcall a call to cgroup_load_subsys(), and in its exitcall a
+call to cgroup_unload_subsys(). It should also set its_subsys.module =
+THIS_MODULE in its .c file.
+
Each subsystem may export the following methods. The only mandatory
methods are create/destroy. Any others that are null are presumed to
be successful no-ops.
newly-created cgroup if an error occurs after this subsystem's
create() method has been called for the new cgroup).
-void pre_destroy(struct cgroup_subsys *ss, struct cgroup *cgrp);
+int pre_destroy(struct cgroup_subsys *ss, struct cgroup *cgrp);
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.
+there are not tasks in the cgroup. If pre_destroy() returns error code,
+rmdir() will fail with it. From this behavior, pre_destroy() can be
+called multiple times against a cgroup.
int can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
- struct task_struct *task)
+ struct task_struct *task, bool threadgroup)
(cgroup_mutex held by caller)
Called prior to moving a task into a cgroup; if the subsystem
task is passed, then a successful result indicates that *any*
unspecified task can be moved into the cgroup. Note that this isn't
called on a fork. If this method returns 0 (success) then this should
-remain valid while the caller holds cgroup_mutex.
+remain valid while the caller holds cgroup_mutex and it is ensured that either
+attach() or cancel_attach() will be called in future. If threadgroup is
+true, then a successful result indicates that all threads in the given
+thread's threadgroup can be moved together.
+
+void cancel_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
+ struct task_struct *task, bool threadgroup)
+(cgroup_mutex held by caller)
+
+Called when a task attach operation has failed after can_attach() has succeeded.
+A subsystem whose can_attach() has some side-effects should provide this
+function, so that the subsystem can implement a rollback. If not, not necessary.
+This will be called only about subsystems whose can_attach() operation have
+succeeded.
void attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
- struct cgroup *old_cgrp, struct task_struct *task)
+ struct cgroup *old_cgrp, struct task_struct *task,
+ bool threadgroup)
(cgroup_mutex held by caller)
Called after the task has been attached to the cgroup, to allow any
post-attachment activity that requires memory allocations or blocking.
+If threadgroup is true, the subsystem should take care of all threads
+in the specified thread's threadgroup. Currently does not support any
+subsystem that might need the old_cgrp for every thread in the group.
void fork(struct cgroup_subsy *ss, struct task_struct *task)
void post_clone(struct cgroup_subsys *ss, struct cgroup *cgrp)
(cgroup_mutex held by caller)
-Called at the end of cgroup_clone() to do any paramater
+Called at the end of cgroup_clone() to do any parameter
initialization which might be required before a task could attach. For
example in cpusets, no task may attach before 'cpus' and 'mems' are set
up.
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff