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Diffstat (limited to 'Documentation/cgroups/cgroups.txt')
| -rw-r--r-- | Documentation/cgroups/cgroups.txt | 310 |
1 files changed, 148 insertions, 162 deletions
diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt index 0ed99f08f1f..821de56d158 100644 --- a/Documentation/cgroups/cgroups.txt +++ b/Documentation/cgroups/cgroups.txt @@ -24,12 +24,12 @@ CONTENTS: 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 3.3 Subsystem API -4. Questions +4. Extended attributes usage +5. Questions 1. Control Groups ================= @@ -62,9 +62,9 @@ an instance of the cgroup virtual filesystem associated with it. 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 +User-level code may create and destroy cgroups by name in an instance of the cgroup virtual file system, specify and query to -which cgroup a task is assigned, and list the task pids assigned to +which cgroup a task is assigned, and list the task PIDs assigned to a cgroup. Those creations and assignments only affect the hierarchy associated with that instance of the cgroup file system. @@ -72,7 +72,7 @@ On their own, the only use for cgroups is for simple job 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/cgroups/cpusets.txt) allows +access. For example, cpusets (see Documentation/cgroups/cpusets.txt) allow you to associate a set of CPUs and a set of memory nodes with the tasks in each cgroup. @@ -80,11 +80,11 @@ tasks in each cgroup. ---------------------------- There are multiple efforts to provide process aggregations in the -Linux kernel, mainly for resource tracking purposes. Such efforts +Linux kernel, mainly for resource-tracking purposes. Such efforts include cpusets, CKRM/ResGroups, UserBeanCounters, and virtual server namespaces. These all require the basic notion of a grouping/partitioning of processes, with newly forked processes ending -in the same group (cgroup) as their parent process. +up in the same group (cgroup) as their parent process. The kernel cgroup patch provides the minimum essential kernel mechanisms required to efficiently implement such groups. It has @@ -127,37 +127,37 @@ following lines: / \ Professors (15%) students (5%) -Browsers like Firefox/Lynx go into the WWW network class, while (k)nfsd go -into NFS network class. +Browsers like Firefox/Lynx go into the WWW network class, while (k)nfsd goes +into the NFS network 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 -(by putting those resource subsystems in different hierarchies) then +(by putting those resource subsystems in different hierarchies), the admin can easily set up a script which receives exec notifications and depending on who is launching the browser he can - # echo browser_pid > /mnt/<restype>/<userclass>/tasks + # echo browser_pid > /sys/fs/cgroup/<restype>/<userclass>/tasks With only a single hierarchy, he now would potentially have to create a separate cgroup for every browser launched and associate it with -approp network and other resource class. This may lead to +appropriate network and other resource class. This may lead to proliferation of such cgroups. -Also lets say that the administrator would like to give enhanced network +Also let's 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 -apps enhanced CPU power, +wants to do online gaming :)) OR give one of the student's simulation +apps enhanced CPU power. -With ability to write pids directly to resource classes, it's just a -matter of : +With ability to write PIDs directly to resource classes, it's just a +matter of: - # echo pid > /mnt/network/<new_class>/tasks + # echo pid > /sys/fs/cgroup/network/<new_class>/tasks (after some time) - # echo pid > /mnt/network/<orig_class>/tasks + # echo pid > /sys/fs/cgroup/network/<orig_class>/tasks -Without this ability, he would have to split the cgroup into +Without this ability, the administrator would have to split the cgroup into multiple separate ones and then associate the new cgroups with the new resource classes. @@ -184,20 +184,20 @@ Control Groups extends the kernel as follows: field of each task_struct using the css_set, anchored at css_set->tasks. - - A cgroup hierarchy filesystem can be mounted for browsing and + - A cgroup hierarchy filesystem can be mounted for browsing and manipulation from user space. - - You can list all the tasks (by pid) attached to any cgroup. + - You can list all the tasks (by PID) attached to any cgroup. The implementation of cgroups requires a few, simple hooks -into the rest of the kernel, none in performance critical paths: +into the rest of the kernel, none in performance-critical paths: - in init/main.c, to initialize the root cgroups and initial css_set at system boot. - in fork and exit, to attach and detach a task from its css_set. -In addition a new file system, of type "cgroup" may be mounted, to +In addition, a new file system of type "cgroup" may be mounted, to enable browsing and modifying the cgroups presently known to the kernel. When mounting a cgroup hierarchy, you may specify a comma-separated list of subsystems to mount as the filesystem mount @@ -230,13 +230,13 @@ as the path relative to the root of the cgroup file system. 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. This list - is not guaranteed to be sorted. Writing a thread id into this file + - 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 + - cgroup.procs: list of thread group IDs 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 thread group id into this file moves all threads in that + Writing a thread group ID into this file moves all threads in that group into this cgroup. - notify_on_release flag: run the release agent on exit? - release_agent: the path to use for release notifications (this file @@ -261,7 +261,7 @@ 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 +desired collection of cgroups then that group is reused, otherwise a new css_set is allocated. The appropriate existing css_set is located by looking into a hash table. @@ -292,17 +292,15 @@ file system) of the abandoned cgroup. This enables automatic removal of abandoned cgroups. The default value of notify_on_release in the root cgroup at system boot is disabled (0). The default value of other cgroups at creation is the current -value of their parents notify_on_release setting. The default value of +value of their parents' notify_on_release settings. The default value of a cgroup hierarchy's release_agent path is empty. 1.5 What does clone_children do ? --------------------------------- -If the clone_children flag is enabled (1) in a cgroup, then all -cgroups created beneath will call the post_clone callbacks for each -subsystem of the newly created cgroup. Usually when this callback is -implemented for a subsystem, it copies the values of the parent -subsystem, this is the case for the cpuset. +This flag only affects the cpuset controller. If the clone_children +flag is enabled (1) in a cgroup, a new cpuset cgroup will copy its +configuration from the parent during initialization. 1.6 How do I use cgroups ? -------------------------- @@ -310,21 +308,24 @@ subsystem, this is the case for the cpuset. To start a new job that is to be contained within a cgroup, using the "cpuset" cgroup subsystem, the steps are something like: - 1) mkdir /dev/cgroup - 2) mount -t cgroup -ocpuset cpuset /dev/cgroup - 3) Create the new cgroup by doing mkdir's and write's (or echo's) in - the /dev/cgroup virtual file system. - 4) Start a task that will be the "founding father" of the new job. - 5) Attach that task to the new cgroup by writing its pid to the - /dev/cgroup tasks file for that cgroup. - 6) fork, exec or clone the job tasks from this founding father task. + 1) mount -t tmpfs cgroup_root /sys/fs/cgroup + 2) mkdir /sys/fs/cgroup/cpuset + 3) mount -t cgroup -ocpuset cpuset /sys/fs/cgroup/cpuset + 4) Create the new cgroup by doing mkdir's and write's (or echo's) in + the /sys/fs/cgroup virtual file system. + 5) Start a task that will be the "founding father" of the new job. + 6) Attach that task to the new cgroup by writing its PID to the + /sys/fs/cgroup/cpuset/tasks file for that cgroup. + 7) fork, exec or clone the job tasks from this founding father task. For example, the following sequence of commands will setup a cgroup named "Charlie", containing just CPUs 2 and 3, and Memory Node 1, and then start a subshell 'sh' in that cgroup: - mount -t cgroup cpuset -ocpuset /dev/cgroup - cd /dev/cgroup + mount -t tmpfs cgroup_root /sys/fs/cgroup + mkdir /sys/fs/cgroup/cpuset + mount -t cgroup cpuset -ocpuset /sys/fs/cgroup/cpuset + cd /sys/fs/cgroup/cpuset mkdir Charlie cd Charlie /bin/echo 2-3 > cpuset.cpus @@ -341,11 +342,11 @@ and then start a subshell 'sh' in that cgroup: 2.1 Basic Usage --------------- -Creating, modifying, using the cgroups can be done through the cgroup +Creating, modifying, using cgroups can be done through the cgroup virtual filesystem. To mount a cgroup hierarchy with all available subsystems, type: -# mount -t cgroup xxx /dev/cgroup +# mount -t cgroup xxx /sys/fs/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. @@ -354,23 +355,29 @@ Note: Some subsystems do not work without some user input first. For instance, if cpusets are enabled the user will have to populate the cpus and mems files for each new cgroup created before that group can be used. -To mount a cgroup hierarchy with just the cpuset and memory -subsystems, type: -# mount -t cgroup -o cpuset,memory hier1 /dev/cgroup +As explained in section `1.2 Why are cgroups needed?' you should create +different hierarchies of cgroups for each single resource or group of +resources you want to control. Therefore, you should mount a tmpfs on +/sys/fs/cgroup and create directories for each cgroup resource or resource +group. -To change the set of subsystems bound to a mounted hierarchy, just -remount with different options: -# mount -o remount,cpuset,blkio hier1 /dev/cgroup +# mount -t tmpfs cgroup_root /sys/fs/cgroup +# mkdir /sys/fs/cgroup/rg1 -Now memory is removed from the hierarchy and blkio is added. +To mount a cgroup hierarchy with just the cpuset and memory +subsystems, type: +# mount -t cgroup -o cpuset,memory hier1 /sys/fs/cgroup/rg1 -Note this will add blkio to the hierarchy but won't remove memory or -cpuset, because the new options are appended to the old ones: -# mount -o remount,blkio /dev/cgroup +While remounting cgroups is currently supported, it is not recommend +to use it. Remounting allows changing bound subsystems and +release_agent. Rebinding is hardly useful as it only works when the +hierarchy is empty and release_agent itself should be replaced with +conventional fsnotify. The support for remounting will be removed in +the future. To Specify a hierarchy's release_agent: # mount -t cgroup -o cpuset,release_agent="/sbin/cpuset_release_agent" \ - xxx /dev/cgroup + xxx /sys/fs/cgroup/rg1 Note that specifying 'release_agent' more than once will return failure. @@ -379,17 +386,17 @@ when the hierarchy consists of a single (root) cgroup. Supporting the ability to arbitrarily bind/unbind subsystems from an existing cgroup hierarchy is intended to be implemented in the future. -Then under /dev/cgroup you can find a tree that corresponds to the -tree of the cgroups in the system. For instance, /dev/cgroup +Then under /sys/fs/cgroup/rg1 you can find a tree that corresponds to the +tree of the cgroups in the system. For instance, /sys/fs/cgroup/rg1 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 +# echo "/sbin/new_release_agent" > /sys/fs/cgroup/rg1/release_agent It can also be changed via remount. -If you want to create a new cgroup under /dev/cgroup: -# cd /dev/cgroup +If you want to create a new cgroup under /sys/fs/cgroup/rg1: +# cd /sys/fs/cgroup/rg1 # mkdir my_cgroup Now you want to do something with this cgroup. @@ -432,9 +439,9 @@ You can attach the current shell task by echoing 0: # echo 0 > tasks You can use the cgroup.procs file instead of the tasks file to move all -threads in a threadgroup at once. Echoing the pid of any task in a +threads in a threadgroup at once. Echoing the PID of any task in a threadgroup to cgroup.procs causes all tasks in that threadgroup to be -be attached to the cgroup. Writing 0 to cgroup.procs moves all tasks +attached to the cgroup. Writing 0 to cgroup.procs moves all tasks in the writing task's threadgroup. Note: Since every task is always a member of exactly one cgroup in each @@ -442,8 +449,8 @@ mounted hierarchy, to remove a task from its current cgroup you must move it into a new cgroup (possibly the root cgroup) by writing to the new cgroup's tasks file. -Note: If the ns cgroup is active, moving a process to another cgroup can -fail. +Note: Due to some restrictions enforced by some cgroup subsystems, moving +a process to another cgroup can fail. 2.3 Mounting hierarchies by name -------------------------------- @@ -464,25 +471,6 @@ 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 ============= @@ -493,7 +481,7 @@ file. See documentation for the subsystem. Each kernel subsystem that wants to hook into the generic cgroup system needs to create a cgroup_subsys object. This contains various methods, which are callbacks from the cgroup system, along -with a subsystem id which will be assigned by the cgroup system. +with a subsystem ID which will be assigned by the cgroup system. Other fields in the cgroup_subsys object include: @@ -507,7 +495,7 @@ Other fields in the cgroup_subsys object include: 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 +indexed by subsystem ID; this pointer is entirely managed by the subsystem; the generic cgroup code will never touch this pointer. 3.2 Synchronization @@ -543,17 +531,16 @@ 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 +methods are css_alloc/free. Any others that are null are presumed to be successful no-ops. -struct cgroup_subsys_state *create(struct cgroup_subsys *ss, - struct cgroup *cgrp) +struct cgroup_subsys_state *css_alloc(struct cgroup *cgrp) (cgroup_mutex held by caller) -Called to create a subsystem state object for a cgroup. The +Called to allocate a subsystem state object for a cgroup. The subsystem should allocate its subsystem state object for the passed cgroup, returning a pointer to the new object on success or a -negative error code. On success, the subsystem pointer should point to +ERR_PTR() value. On success, the subsystem pointer should point to a structure of type cgroup_subsys_state (typically embedded in a larger subsystem-specific object), which will be initialized by the cgroup system. Note that this will be called at initialization to @@ -562,109 +549,108 @@ identified by the passed cgroup object having a NULL parent (since it's the root of the hierarchy) and may be an appropriate place for initialization code. -void destroy(struct cgroup_subsys *ss, struct cgroup *cgrp) +int css_online(struct cgroup *cgrp) (cgroup_mutex held by caller) -The cgroup system is about to destroy the passed cgroup; the subsystem -should do any necessary cleanup and free its subsystem state -object. By the time this method is called, the cgroup has already been -unlinked from the file system and from the child list of its parent; -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). +Called after @cgrp successfully completed all allocations and made +visible to cgroup_for_each_child/descendant_*() iterators. The +subsystem may choose to fail creation by returning -errno. This +callback can be used to implement reliable state sharing and +propagation along the hierarchy. See the comment on +cgroup_for_each_descendant_pre() for details. -int pre_destroy(struct cgroup_subsys *ss, struct cgroup *cgrp); +void css_offline(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. If pre_destroy() returns error code, -rmdir() will fail with it. From this behavior, pre_destroy() can be -called multiple times against a cgroup. +This is the counterpart of css_online() and called iff css_online() +has succeeded on @cgrp. This signifies the beginning of the end of +@cgrp. @cgrp is being removed and the subsystem should start dropping +all references it's holding on @cgrp. When all references are dropped, +cgroup removal will proceed to the next step - css_free(). After this +callback, @cgrp should be considered dead to the subsystem. -int can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp, - struct task_struct *task) +void css_free(struct cgroup *cgrp) (cgroup_mutex held by caller) -Called prior to moving a task into a cgroup; if the subsystem -returns an error, this will abort the attach operation. If a NULL -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 and it is ensured that either -attach() or cancel_attach() will be called in future. +The cgroup system is about to free @cgrp; the subsystem should free +its subsystem state object. By the time this method is called, @cgrp +is completely unused; @cgrp->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). -int can_attach_task(struct cgroup *cgrp, struct task_struct *tsk); +int can_attach(struct cgroup *cgrp, struct cgroup_taskset *tset) (cgroup_mutex held by caller) -As can_attach, but for operations that must be run once per task to be -attached (possibly many when using cgroup_attach_proc). Called after -can_attach. +Called prior to moving one or more tasks into a cgroup; if the +subsystem returns an error, this will abort the attach operation. +@tset contains the tasks to be attached and is guaranteed to have at +least one task in it. + +If there are multiple tasks in the taskset, then: + - it's guaranteed that all are from the same thread group + - @tset contains all tasks from the thread group whether or not + they're switching cgroups + - the first task is the leader + +Each @tset entry also contains the task's old cgroup and tasks which +aren't switching cgroup can be skipped easily using the +cgroup_taskset_for_each() iterator. 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 and it is ensured that either +attach() or cancel_attach() will be called in future. -void cancel_attach(struct cgroup_subsys *ss, struct cgroup *cgrp, - struct task_struct *task, bool threadgroup) +void cancel_attach(struct cgroup *cgrp, struct cgroup_taskset *tset) (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 pre_attach(struct cgroup *cgrp); -(cgroup_mutex held by caller) +succeeded. The parameters are identical to can_attach(). -For any non-per-thread attachment work that needs to happen before -attach_task. Needed by cpuset. - -void attach(struct cgroup_subsys *ss, struct cgroup *cgrp, - struct cgroup *old_cgrp, struct task_struct *task) +void attach(struct cgroup *cgrp, struct cgroup_taskset *tset) (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. +The parameters are identical to can_attach(). -void attach_task(struct cgroup *cgrp, struct task_struct *tsk); -(cgroup_mutex held by caller) - -As attach, but for operations that must be run once per task to be attached, -like can_attach_task. Called before attach. 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 fork(struct task_struct *task) Called when a task is forked into a cgroup. -void exit(struct cgroup_subsys *ss, struct task_struct *task) +void exit(struct task_struct *task) Called during task exit. -int populate(struct cgroup_subsys *ss, struct cgroup *cgrp) -(cgroup_mutex held by caller) - -Called after creation of a cgroup to allow a subsystem to populate -the cgroup directory with file entries. The subsystem should make -calls to cgroup_add_file() with objects of type cftype (see -include/linux/cgroup.h for details). Note that although this -method can return an error code, the error code is currently not -always handled well. - -void post_clone(struct cgroup_subsys *ss, struct cgroup *cgrp) +void bind(struct cgroup *root) (cgroup_mutex held by caller) -Called during cgroup_create() 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. - -void bind(struct cgroup_subsys *ss, struct cgroup *root) -(cgroup_mutex and ss->hierarchy_mutex held by caller) - Called when a cgroup subsystem is rebound to a different hierarchy and root cgroup. Currently this will only involve movement between the default hierarchy (which never has sub-cgroups) and a hierarchy that is being created/destroyed (and hence has no sub-cgroups). -4. Questions +4. Extended attribute usage +=========================== + +cgroup filesystem supports certain types of extended attributes in its +directories and files. The current supported types are: + - Trusted (XATTR_TRUSTED) + - Security (XATTR_SECURITY) + +Both require CAP_SYS_ADMIN capability to set. + +Like in tmpfs, the extended attributes in cgroup filesystem are stored +using kernel memory and it's advised to keep the usage at minimum. This +is the reason why user defined extended attributes are not supported, since +any user can do it and there's no limit in the value size. + +The current known users for this feature are SELinux to limit cgroup usage +in containers and systemd for assorted meta data like main PID in a cgroup +(systemd creates a cgroup per service). + +5. Questions ============ Q: what's up with this '/bin/echo' ? @@ -674,5 +660,5 @@ A: bash's builtin 'echo' command does not check calls to write() against Q: When I attach processes, only the first of the line gets really attached ! A: We can only return one error code per call to write(). So you should also - put only ONE pid. + put only ONE PID. |