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-rw-r--r--Documentation/cgroups/cgroups.txt42
1 files changed, 29 insertions, 13 deletions
diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index d9e5d6f41b92..6eb1a97e88ce 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -56,7 +56,7 @@ hierarchy, and a set of subsystems; each subsystem has system-specific
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
@@ -124,10 +124,10 @@ following lines:
/ \
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
@@ -252,10 +252,8 @@ cgroup file system directories.
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;
@@ -327,7 +325,7 @@ and then start a subshell 'sh' in that cgroup:
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
@@ -335,12 +333,23 @@ The "xxx" is not interpreted by the cgroup code, but will appear in
To mount a cgroup hierarchy with just the cpuset and numtasks
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
@@ -351,6 +360,11 @@ Then under /dev/cgroup you can find a tree that corresponds to the
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
@@ -478,11 +492,13 @@ cgroup->parent is still valid. (Note - can also be called for a
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)
@@ -523,7 +539,7 @@ always handled well.
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.