Blame view
Documentation/cgroups/cgroups.txt
26.3 KB
ddbcc7e8e Task Control Grou... |
1 2 |
CGROUPS ------- |
45ce80fb6 cgroups: consolid... |
3 4 |
Written by Paul Menage <menage@google.com> based on Documentation/cgroups/cpusets.txt |
ddbcc7e8e Task Control Grou... |
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 |
Original copyright statements from cpusets.txt: Portions Copyright (C) 2004 BULL SA. Portions Copyright (c) 2004-2006 Silicon Graphics, Inc. Modified by Paul Jackson <pj@sgi.com> Modified by Christoph Lameter <clameter@sgi.com> CONTENTS: ========= 1. Control Groups 1.1 What are cgroups ? 1.2 Why are cgroups needed ? 1.3 How are cgroups implemented ? 1.4 What does notify_on_release do ? |
97978e6d1 cgroup: add clone... |
20 21 |
1.5 What does clone_children do ? 1.6 How do I use cgroups ? |
ddbcc7e8e Task Control Grou... |
22 23 24 |
2. Usage Examples and Syntax 2.1 Basic Usage 2.2 Attaching processes |
8ca712ea8 cgroups: fix CONT... |
25 |
2.3 Mounting hierarchies by name |
0dea11687 cgroup: implement... |
26 |
2.4 Notification API |
ddbcc7e8e Task Control Grou... |
27 28 29 30 31 32 33 |
3. Kernel API 3.1 Overview 3.2 Synchronization 3.3 Subsystem API 4. Questions 1. Control Groups |
d19e05833 cgroup: fix and u... |
34 |
================= |
ddbcc7e8e Task Control Grou... |
35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 |
1.1 What are cgroups ? ---------------------- Control Groups provide a mechanism for aggregating/partitioning sets of tasks, and all their future children, into hierarchical groups with specialized behaviour. Definitions: A *cgroup* associates a set of tasks with a set of parameters for one or more subsystems. A *subsystem* is a module that makes use of the task grouping facilities provided by cgroups to treat groups of tasks in particular ways. A subsystem is typically a "resource controller" that schedules a resource or applies per-cgroup limits, but it may be anything that wants to act on a group of processes, e.g. a virtualization subsystem. A *hierarchy* is a set of cgroups arranged in a tree, such that every task in the system is in exactly one of the cgroups in the 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. |
caa790ba6 trivial: cgroups:... |
60 |
At any one time there may be multiple active hierarchies of task |
ddbcc7e8e Task Control Grou... |
61 62 63 64 65 66 67 68 69 70 71 72 |
cgroups. Each hierarchy is a partition of all tasks in the system. 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 a cgroup. Those creations and assignments only affect the hierarchy associated with that instance of the cgroup file system. 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 |
45ce80fb6 cgroups: consolid... |
73 |
access. For example, cpusets (see Documentation/cgroups/cpusets.txt) allows |
ddbcc7e8e Task Control Grou... |
74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 |
you to associate a set of CPUs and a set of memory nodes with the tasks in each cgroup. 1.2 Why are cgroups needed ? ---------------------------- There are multiple efforts to provide process aggregations in the 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. The kernel cgroup patch provides the minimum essential kernel mechanisms required to efficiently implement such groups. It has minimal impact on the system fast paths, and provides hooks for specific subsystems such as cpusets to provide additional behaviour as desired. Multiple hierarchy support is provided to allow for situations where the division of tasks into cgroups is distinctly different for different subsystems - having parallel hierarchies allows each hierarchy to be a natural division of tasks, without having to handle complex combinations of tasks that would be present if several unrelated subsystems needed to be forced into the same tree of cgroups. At one extreme, each resource controller or subsystem could be in a separate hierarchy; at the other extreme, all subsystems would be attached to the same hierarchy. As an example of a scenario (originally proposed by vatsa@in.ibm.com) that can benefit from multiple hierarchies, consider a large university server with various users - students, professors, system tasks etc. The resource planning for this server could be along the following lines: |
6ad85239d Documentation: up... |
110 |
CPU : "Top cpuset" |
ddbcc7e8e Task Control Grou... |
111 112 |
/ \ CPUSet1 CPUSet2 |
6ad85239d Documentation: up... |
113 114 |
| | (Professors) (Students) |
ddbcc7e8e Task Control Grou... |
115 116 117 |
In addition (system tasks) are attached to topcpuset (so that they can run anywhere) with a limit of 20% |
6ad85239d Documentation: up... |
118 |
Memory : Professors (50%), Students (30%), system (20%) |
ddbcc7e8e Task Control Grou... |
119 |
|
6ad85239d Documentation: up... |
120 |
Disk : Professors (50%), Students (30%), system (20%) |
ddbcc7e8e Task Control Grou... |
121 122 123 |
Network : WWW browsing (20%), Network File System (60%), others (20%) / \ |
6ad85239d Documentation: up... |
124 |
Professors (15%) students (5%) |
ddbcc7e8e Task Control Grou... |
125 |
|
caa790ba6 trivial: cgroups:... |
126 |
Browsers like Firefox/Lynx go into the WWW network class, while (k)nfsd go |
ddbcc7e8e Task Control Grou... |
127 |
into NFS network class. |
caa790ba6 trivial: cgroups:... |
128 |
At the same time Firefox/Lynx will share an appropriate CPU/Memory class |
ddbcc7e8e Task Control Grou... |
129 130 131 132 133 134 |
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 the admin can easily set up a script which receives exec notifications and depending on who is launching the browser he can |
f6e07d380 Documentation: up... |
135 |
# echo browser_pid > /sys/fs/cgroup/<restype>/<userclass>/tasks |
ddbcc7e8e Task Control Grou... |
136 137 138 |
With only a single hierarchy, he now would potentially have to create a separate cgroup for every browser launched and associate it with |
67de0162f Documentation: fi... |
139 |
appropriate network and other resource class. This may lead to |
ddbcc7e8e Task Control Grou... |
140 141 142 143 |
proliferation of such cgroups. 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 |
d19e05833 cgroup: fix and u... |
144 |
wants to do online gaming :)) OR give one of the students simulation |
ddbcc7e8e Task Control Grou... |
145 |
apps enhanced CPU power, |
d19e05833 cgroup: fix and u... |
146 |
With ability to write pids directly to resource classes, it's just a |
ddbcc7e8e Task Control Grou... |
147 |
matter of : |
f6e07d380 Documentation: up... |
148 |
# echo pid > /sys/fs/cgroup/network/<new_class>/tasks |
ddbcc7e8e Task Control Grou... |
149 |
(after some time) |
f6e07d380 Documentation: up... |
150 |
# echo pid > /sys/fs/cgroup/network/<orig_class>/tasks |
ddbcc7e8e Task Control Grou... |
151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 |
Without this ability, he would have to split the cgroup into multiple separate ones and then associate the new cgroups with the new resource classes. 1.3 How are cgroups implemented ? --------------------------------- Control Groups extends the kernel as follows: - Each task in the system has a reference-counted pointer to a css_set. - A css_set contains a set of reference-counted pointers to cgroup_subsys_state objects, one for each cgroup subsystem registered in the system. There is no direct link from a task to the cgroup of which it's a member in each hierarchy, but this can be determined by following pointers through the cgroup_subsys_state objects. This is because accessing the subsystem state is something that's expected to happen frequently and in performance-critical code, whereas operations that require a task's actual cgroup assignments (in particular, moving between |
817929ec2 Task Control Grou... |
175 176 177 |
cgroups) are less common. A linked list runs through the cg_list field of each task_struct using the css_set, anchored at css_set->tasks. |
ddbcc7e8e Task Control Grou... |
178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 |
- 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. The implementation of cgroups requires a few, simple hooks 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 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 options. By default, mounting the cgroup filesystem attempts to mount a hierarchy containing all registered subsystems. If an active hierarchy with exactly the same set of subsystems already exists, it will be reused for the new mount. If no existing hierarchy matches, and any of the requested subsystems are in use in an existing hierarchy, the mount will fail with -EBUSY. Otherwise, a new hierarchy is activated, associated with the requested subsystems. It's not currently possible to bind a new subsystem to an active cgroup hierarchy, or to unbind a subsystem from an active cgroup hierarchy. This may be possible in future, but is fraught with nasty error-recovery issues. When a cgroup filesystem is unmounted, if there are any child cgroups created below the top-level cgroup, that hierarchy will remain active even though unmounted; if there are no child cgroups then the hierarchy will be deactivated. No new system calls are added for cgroups - all support for querying and modifying cgroups is via this cgroup file system. Each task under /proc has an added file named 'cgroup' displaying, for each active hierarchy, the subsystem names and the cgroup name 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: |
7823da36c cgroups: update d... |
224 225 226 227 228 229 |
- 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. |
74a1166df cgroups: make pro... |
230 231 |
Writing a thread group id into this file moves all threads in that group into this cgroup. |
d19e05833 cgroup: fix and u... |
232 233 234 |
- 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) |
ddbcc7e8e Task Control Grou... |
235 236 |
Other subsystems such as cpusets may add additional files in each |
d19e05833 cgroup: fix and u... |
237 |
cgroup dir. |
ddbcc7e8e Task Control Grou... |
238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 |
New cgroups are created using the mkdir system call or shell command. The properties of a cgroup, such as its flags, are modified by writing to the appropriate file in that cgroups directory, as listed above. The named hierarchical structure of nested cgroups allows partitioning a large system into nested, dynamically changeable, "soft-partitions". The attachment of each task, automatically inherited at fork by any children of that task, to a cgroup allows organizing the work load on a system into related sets of tasks. A task may be re-attached to any other cgroup, if allowed by the permissions on the necessary 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 |
b851ee792 cgroups: update d... |
256 257 |
css_set is allocated. The appropriate existing css_set is located by looking into a hash table. |
ddbcc7e8e Task Control Grou... |
258 |
|
817929ec2 Task Control Grou... |
259 260 261 |
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 |
d19e05833 cgroup: fix and u... |
262 |
a single cgroup on its cgrp_link_list field, and a list of |
817929ec2 Task Control Grou... |
263 264 265 266 267 |
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 each css_set that references the cgroup, and sub-iterating over each css_set's task set. |
ddbcc7e8e Task Control Grou... |
268 269 270 271 272 273 |
The use of a Linux virtual file system (vfs) to represent the cgroup hierarchy provides for a familiar permission and name space for cgroups, with a minimum of additional kernel code. 1.4 What does notify_on_release do ? ------------------------------------ |
ddbcc7e8e Task Control Grou... |
274 275 276 277 278 279 280 281 282 283 284 285 |
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 is removed, then the kernel runs the command specified by the contents of the "release_agent" file in that hierarchy's root directory, supplying the pathname (relative to the mount point of the cgroup 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 a cgroup hierarchy's release_agent path is empty. |
97978e6d1 cgroup: add clone... |
286 287 288 289 290 291 292 293 294 295 |
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. 1.6 How do I use cgroups ? |
ddbcc7e8e Task Control Grou... |
296 297 298 299 |
-------------------------- To start a new job that is to be contained within a cgroup, using the "cpuset" cgroup subsystem, the steps are something like: |
f6e07d380 Documentation: up... |
300 301 302 303 304 305 306 307 308 |
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. |
ddbcc7e8e Task Control Grou... |
309 310 311 312 |
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: |
f6e07d380 Documentation: up... |
313 314 315 316 |
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 |
ddbcc7e8e Task Control Grou... |
317 318 |
mkdir Charlie cd Charlie |
0f146a764 cgroups: fix docu... |
319 320 |
/bin/echo 2-3 > cpuset.cpus /bin/echo 1 > cpuset.mems |
ddbcc7e8e Task Control Grou... |
321 322 323 324 325 326 327 328 329 330 331 332 333 334 |
/bin/echo $$ > tasks sh # The subshell 'sh' is now running in cgroup Charlie # The next line should display '/Charlie' cat /proc/self/cgroup 2. Usage Examples and Syntax ============================ 2.1 Basic Usage --------------- Creating, modifying, using the cgroups can be done through the cgroup virtual filesystem. |
caa790ba6 trivial: cgroups:... |
335 |
To mount a cgroup hierarchy with all available subsystems, type: |
f6e07d380 Documentation: up... |
336 |
# mount -t cgroup xxx /sys/fs/cgroup |
ddbcc7e8e Task Control Grou... |
337 338 339 |
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. |
bb6405eab Documentation: up... |
340 341 342 |
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. |
f6e07d380 Documentation: up... |
343 344 345 346 347 348 349 350 |
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. # mount -t tmpfs cgroup_root /sys/fs/cgroup # mkdir /sys/fs/cgroup/rg1 |
595f4b694 Documentation/cgr... |
351 |
To mount a cgroup hierarchy with just the cpuset and memory |
ddbcc7e8e Task Control Grou... |
352 |
subsystems, type: |
f6e07d380 Documentation: up... |
353 |
# mount -t cgroup -o cpuset,memory hier1 /sys/fs/cgroup/rg1 |
ddbcc7e8e Task Control Grou... |
354 355 356 |
To change the set of subsystems bound to a mounted hierarchy, just remount with different options: |
f6e07d380 Documentation: up... |
357 |
# mount -o remount,cpuset,blkio hier1 /sys/fs/cgroup/rg1 |
ddbcc7e8e Task Control Grou... |
358 |
|
1bdcd78e2 cgroups: remove d... |
359 |
Now memory is removed from the hierarchy and blkio is added. |
b6719ec1a cgroups: more doc... |
360 |
|
1bdcd78e2 cgroups: remove d... |
361 |
Note this will add blkio to the hierarchy but won't remove memory or |
b6719ec1a cgroups: more doc... |
362 |
cpuset, because the new options are appended to the old ones: |
f6e07d380 Documentation: up... |
363 |
# mount -o remount,blkio /sys/fs/cgroup/rg1 |
b6719ec1a cgroups: more doc... |
364 365 366 |
To Specify a hierarchy's release_agent: # mount -t cgroup -o cpuset,release_agent="/sbin/cpuset_release_agent" \ |
f6e07d380 Documentation: up... |
367 |
xxx /sys/fs/cgroup/rg1 |
b6719ec1a cgroups: more doc... |
368 369 |
Note that specifying 'release_agent' more than once will return failure. |
ddbcc7e8e Task Control Grou... |
370 371 372 373 374 |
Note that changing the set of subsystems is currently only supported 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. |
f6e07d380 Documentation: up... |
375 376 |
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 |
ddbcc7e8e Task Control Grou... |
377 |
is the cgroup that holds the whole system. |
b6719ec1a cgroups: more doc... |
378 |
If you want to change the value of release_agent: |
f6e07d380 Documentation: up... |
379 |
# echo "/sbin/new_release_agent" > /sys/fs/cgroup/rg1/release_agent |
b6719ec1a cgroups: more doc... |
380 381 |
It can also be changed via remount. |
f6e07d380 Documentation: up... |
382 383 |
If you want to create a new cgroup under /sys/fs/cgroup/rg1: # cd /sys/fs/cgroup/rg1 |
ddbcc7e8e Task Control Grou... |
384 385 386 387 388 389 390 |
# mkdir my_cgroup Now you want to do something with this cgroup. # cd my_cgroup In this directory you can find several files: # ls |
7823da36c cgroups: update d... |
391 |
cgroup.procs notify_on_release tasks |
d19e05833 cgroup: fix and u... |
392 |
(plus whatever files added by the attached subsystems) |
ddbcc7e8e Task Control Grou... |
393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 |
Now attach your shell to this cgroup: # /bin/echo $$ > tasks You can also create cgroups inside your cgroup by using mkdir in this directory. # mkdir my_sub_cs To remove a cgroup, just use rmdir: # rmdir my_sub_cs This will fail if the cgroup is in use (has cgroups inside, or has processes attached, or is held alive by other subsystem-specific reference). 2.2 Attaching processes ----------------------- # /bin/echo PID > tasks Note that it is PID, not PIDs. You can only attach ONE task at a time. If you have several tasks to attach, you have to do it one after another: # /bin/echo PID1 > tasks # /bin/echo PID2 > tasks ... # /bin/echo PIDn > tasks |
bef67c5a7 cgroups: document... |
420 421 422 |
You can attach the current shell task by echoing 0: # echo 0 > tasks |
74a1166df cgroups: make pro... |
423 424 425 426 427 |
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 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 in the writing task's threadgroup. |
bb6405eab Documentation: up... |
428 429 430 431 |
Note: Since every task is always a member of exactly one cgroup in each 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. |
5fe69d7e2 Documentation: up... |
432 433 |
Note: Due to some restrictions enforced by some cgroup subsystems, moving a process to another cgroup can fail. |
bb6405eab Documentation: up... |
434 |
|
c6d57f331 cgroups: support ... |
435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 |
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. |
0dea11687 cgroup: implement... |
453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 |
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. |
c6d57f331 cgroups: support ... |
472 |
|
ddbcc7e8e Task Control Grou... |
473 474 475 476 477 478 479 480 481 482 483 484 485 486 |
3. Kernel API ============= 3.1 Overview ------------ 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. Other fields in the cgroup_subsys object include: - subsys_id: a unique array index for the subsystem, indicating which |
d19e05833 cgroup: fix and u... |
487 |
entry in cgroup->subsys[] this subsystem should be managing. |
ddbcc7e8e Task Control Grou... |
488 |
|
d19e05833 cgroup: fix and u... |
489 490 |
- name: should be initialized to a unique subsystem name. Should be no longer than MAX_CGROUP_TYPE_NAMELEN. |
ddbcc7e8e Task Control Grou... |
491 |
|
d19e05833 cgroup: fix and u... |
492 493 |
- early_init: indicate if the subsystem needs early initialization at system boot. |
ddbcc7e8e Task Control Grou... |
494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 |
Each cgroup object created by the system has an array of pointers, indexed by subsystem id; this pointer is entirely managed by the subsystem; the generic cgroup code will never touch this pointer. 3.2 Synchronization ------------------- There is a global mutex, cgroup_mutex, used by the cgroup system. This should be taken by anything that wants to modify a cgroup. It may also be taken to prevent cgroups from being modified, but more specific locks may be more appropriate in that situation. See kernel/cgroup.c for more details. Subsystems can take/release the cgroup_mutex via the functions |
ddbcc7e8e Task Control Grou... |
511 512 513 514 515 516 517 518 |
cgroup_lock()/cgroup_unlock(). Accessing a task's cgroup pointer may be done in the following ways: - while holding cgroup_mutex - while holding the task's alloc_lock (via task_lock()) - inside an rcu_read_lock() section via rcu_dereference() 3.3 Subsystem API |
d19e05833 cgroup: fix and u... |
519 |
----------------- |
ddbcc7e8e Task Control Grou... |
520 521 522 523 524 |
Each subsystem should: - add an entry in linux/cgroup_subsys.h - define a cgroup_subsys object called <name>_subsys |
e6a1105ba cgroups: subsyste... |
525 |
If a subsystem can be compiled as a module, it should also have in its |
cf5d5941f cgroups: subsyste... |
526 527 528 |
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. |
e6a1105ba cgroups: subsyste... |
529 |
|
ddbcc7e8e Task Control Grou... |
530 531 532 |
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. |
d19e05833 cgroup: fix and u... |
533 534 |
struct cgroup_subsys_state *create(struct cgroup_subsys *ss, struct cgroup *cgrp) |
8dc4f3e17 cgroups: move cgr... |
535 |
(cgroup_mutex held by caller) |
ddbcc7e8e Task Control Grou... |
536 537 538 539 540 541 542 543 544 545 546 547 |
Called to create 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 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 create the root subsystem state for this subsystem; this case can be 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. |
d19e05833 cgroup: fix and u... |
548 |
void destroy(struct cgroup_subsys *ss, struct cgroup *cgrp) |
8dc4f3e17 cgroups: move cgr... |
549 |
(cgroup_mutex held by caller) |
ddbcc7e8e Task Control Grou... |
550 |
|
8dc4f3e17 cgroups: move cgr... |
551 552 553 554 555 556 557 |
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). |
ddbcc7e8e Task Control Grou... |
558 |
|
ec64f5154 cgroup: fix frequ... |
559 |
int pre_destroy(struct cgroup_subsys *ss, struct cgroup *cgrp); |
d19e05833 cgroup: fix and u... |
560 561 562 |
Called before checking the reference count on each subsystem. This may be useful for subsystems which have some extra references even if |
ec64f5154 cgroup: fix frequ... |
563 564 565 |
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. |
d19e05833 cgroup: fix and u... |
566 567 |
int can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp, |
2f7ee5691 cgroup: introduce... |
568 |
struct cgroup_taskset *tset) |
8dc4f3e17 cgroups: move cgr... |
569 |
(cgroup_mutex held by caller) |
ddbcc7e8e Task Control Grou... |
570 |
|
2f7ee5691 cgroup: introduce... |
571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 |
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 |
f780bdb7c cgroups: add per-... |
587 |
attach() or cancel_attach() will be called in future. |
2468c7234 cgroup: introduce... |
588 |
void cancel_attach(struct cgroup_subsys *ss, struct cgroup *cgrp, |
2f7ee5691 cgroup: introduce... |
589 |
struct cgroup_taskset *tset) |
2468c7234 cgroup: introduce... |
590 591 592 593 |
(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 |
883931612 Fix typos in comm... |
594 |
function, so that the subsystem can implement a rollback. If not, not necessary. |
2468c7234 cgroup: introduce... |
595 |
This will be called only about subsystems whose can_attach() operation have |
2f7ee5691 cgroup: introduce... |
596 |
succeeded. The parameters are identical to can_attach(). |
2468c7234 cgroup: introduce... |
597 |
|
d19e05833 cgroup: fix and u... |
598 |
void attach(struct cgroup_subsys *ss, struct cgroup *cgrp, |
2f7ee5691 cgroup: introduce... |
599 |
struct cgroup_taskset *tset) |
18e7f1f0d cgroups: document... |
600 |
(cgroup_mutex held by caller) |
ddbcc7e8e Task Control Grou... |
601 602 603 |
Called after the task has been attached to the cgroup, to allow any post-attachment activity that requires memory allocations or blocking. |
2f7ee5691 cgroup: introduce... |
604 |
The parameters are identical to can_attach(). |
f780bdb7c cgroups: add per-... |
605 |
|
ddbcc7e8e Task Control Grou... |
606 |
void fork(struct cgroup_subsy *ss, struct task_struct *task) |
ddbcc7e8e Task Control Grou... |
607 |
|
e8d55fdeb cgroups: simplify... |
608 |
Called when a task is forked into a cgroup. |
ddbcc7e8e Task Control Grou... |
609 610 |
void exit(struct cgroup_subsys *ss, struct task_struct *task) |
ddbcc7e8e Task Control Grou... |
611 |
|
d19e05833 cgroup: fix and u... |
612 |
Called during task exit. |
ddbcc7e8e Task Control Grou... |
613 |
|
d19e05833 cgroup: fix and u... |
614 |
int populate(struct cgroup_subsys *ss, struct cgroup *cgrp) |
18e7f1f0d cgroups: document... |
615 |
(cgroup_mutex held by caller) |
ddbcc7e8e Task Control Grou... |
616 617 618 619 620 621 622 |
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. |
d19e05833 cgroup: fix and u... |
623 |
void post_clone(struct cgroup_subsys *ss, struct cgroup *cgrp) |
18e7f1f0d cgroups: document... |
624 |
(cgroup_mutex held by caller) |
697f41610 Task Control Grou... |
625 |
|
a77aea920 cgroup: remove th... |
626 |
Called during cgroup_create() to do any parameter |
697f41610 Task Control Grou... |
627 628 629 |
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. |
ddbcc7e8e Task Control Grou... |
630 |
void bind(struct cgroup_subsys *ss, struct cgroup *root) |
999cd8a45 cgroups: add a pe... |
631 |
(cgroup_mutex and ss->hierarchy_mutex held by caller) |
ddbcc7e8e Task Control Grou... |
632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 |
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 ============ Q: what's up with this '/bin/echo' ? A: bash's builtin 'echo' command does not check calls to write() against errors. If you use it in the cgroup file system, you won't be able to tell whether a command succeeded or failed. 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. |