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
/ \
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.
+ Writing a tgid into this file moves all threads with that tgid into
+ this cgroup.
- 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)
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
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.
+
+
3. Kernel API
=============
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. If threadgroup is
+true, then a successful result indicates that all threads in the given
+thread's threadgroup can be moved together.
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.