Diffstat (limited to 'Documentation/cgroups')
8 files changed, 316 insertions, 163 deletions
diff --git a/Documentation/cgroups/00-INDEX b/Documentation/cgroups/00-INDEX
index 3f58fa3d6d0..f78b90a35ad 100644
@@ -1,7 +1,11 @@
- this file
+ - Description for Block IO Controller, implementation and usage details.
- Control Groups definition, implementation details, examples and API.
+ - A user program for cgroup listener.
- CPU Accounting Controller; account CPU usage for groups of tasks.
@@ -10,9 +14,13 @@ devices.txt
- Device Whitelist Controller; description, interface and security.
- checkpointing; rationale to not use signals, interface.
+ - HugeTLB Controller implementation and usage details.
- Memory Resource Controller; implementation details.
- Memory Resource Controller; design, accounting, interface, testing.
+ - Network priority cgroups details and usages.
- Resource Counter API.
diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index 8e74980ab38..bcf1a00b06a 100644
@@ -29,7 +29,8 @@ CONTENTS:
3.3 Subsystem API
+4. Extended attributes usage
1. Control Groups
@@ -62,9 +63,9 @@ 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 +73,7 @@ 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 +81,11 @@ 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
@@ -127,14 +128,14 @@ 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
@@ -145,19 +146,19 @@ a separate cgroup for every browser launched and associate it with
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
# echo pid > /sys/fs/cgroup/network/<new_class>/tasks
(after some time)
# 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 +185,20 @@ Control Groups extends the kernel as follows:
field of each task_struct using the css_set, anchored at
- - 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 +231,13 @@ 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 +262,7 @@ 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 +293,15 @@ 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 ?
@@ -316,7 +315,7 @@ the "cpuset" cgroup subsystem, the steps are something like:
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
+ 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.
@@ -344,7 +343,7 @@ 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
To mount a cgroup hierarchy with all available subsystems, type:
@@ -370,15 +369,12 @@ To mount a cgroup hierarchy with just the cpuset and memory
# mount -t cgroup -o cpuset,memory hier1 /sys/fs/cgroup/rg1
-To change the set of subsystems bound to a mounted hierarchy, just
-remount with different options:
-# mount -o remount,cpuset,blkio hier1 /sys/fs/cgroup/rg1
-Now memory is removed from the hierarchy and blkio is added.
-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 /sys/fs/cgroup/rg1
+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
To Specify a hierarchy's release_agent:
# mount -t cgroup -o cpuset,release_agent="/sbin/cpuset_release_agent" \
@@ -444,7 +440,7 @@ 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
in the writing task's threadgroup.
@@ -482,7 +478,7 @@ in /proc/mounts and /proc/<pid>/cgroups.
There is mechanism which allows to get notifications about changing
status of a cgroup.
-To register new notification handler you need:
+To register a new notification handler you need to:
- 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.
@@ -491,7 +487,7 @@ To register new notification handler you need:
eventfd will be woken up by control file implementation or when the
cgroup is removed.
-To unregister notification handler just close eventfd.
+To unregister a notification handler just close eventfd.
NOTE: Support of notifications should be implemented for the control
file. See documentation for the subsystem.
@@ -505,7 +501,7 @@ 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:
@@ -519,7 +515,7 @@ 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.
@@ -555,16 +551,16 @@ 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 *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
@@ -573,24 +569,33 @@ 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
-void destroy(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.
+void css_offline(struct cgroup *cgrp);
-int pre_destroy(struct cgroup *cgrp);
+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.
+void css_free(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.
+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(struct cgroup *cgrp, struct cgroup_taskset *tset)
(cgroup_mutex held by caller)
@@ -637,33 +642,34 @@ void exit(struct task_struct *task)
Called during task exit.
-int populate(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 *cgrp)
-(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
void bind(struct cgroup *root)
-(cgroup_mutex and ss->hierarchy_mutex held by caller)
+(cgroup_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. 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).
Q: what's up with this '/bin/echo' ?
@@ -673,5 +679,5 @@ 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.
diff --git a/Documentation/cgroups/cpusets.txt b/Documentation/cgroups/cpusets.txt
index cefd3d8bbd1..12e01d432bf 100644
@@ -218,7 +218,7 @@ and name space for cpusets, with a minimum of additional kernel code.
The cpus and mems files in the root (top_cpuset) cpuset are
read-only. The cpus file automatically tracks the value of
cpu_online_mask using a CPU hotplug notifier, and the mems file
-automatically tracks the value of node_states[N_HIGH_MEMORY]--i.e.,
+automatically tracks the value of node_states[N_MEMORY]--i.e.,
nodes with memory--using the cpuset_track_online_nodes() hook.
diff --git a/Documentation/cgroups/freezer-subsystem.txt b/Documentation/cgroups/freezer-subsystem.txt
index 7e62de1e59f..c96a72cbb30 100644
@@ -49,13 +49,49 @@ prevent the freeze/unfreeze cycle from becoming visible to the tasks
being frozen. This allows the bash example above and gdb to run as
-The freezer subsystem in the container filesystem defines a file named
-freezer.state. Writing "FROZEN" to the state file will freeze all tasks in the
-cgroup. Subsequently writing "THAWED" will unfreeze the tasks in the cgroup.
-Reading will return the current state.
+The cgroup freezer is hierarchical. Freezing a cgroup freezes all
+tasks beloning to the cgroup and all its descendant cgroups. Each
+cgroup has its own state (self-state) and the state inherited from the
+parent (parent-state). Iff both states are THAWED, the cgroup is
-Note freezer.state doesn't exist in root cgroup, which means root cgroup
+The following cgroupfs files are created by cgroup freezer.
+* freezer.state: Read-write.
+ When read, returns the effective state of the cgroup - "THAWED",
+ "FREEZING" or "FROZEN". This is the combined self and parent-states.
+ If any is freezing, the cgroup is freezing (FREEZING or FROZEN).
+ FREEZING cgroup transitions into FROZEN state when all tasks
+ belonging to the cgroup and its descendants become frozen. Note that
+ a cgroup reverts to FREEZING from FROZEN after a new task is added
+ to the cgroup or one of its descendant cgroups until the new task is
+ When written, sets the self-state of the cgroup. Two values are
+ allowed - "FROZEN" and "THAWED". If FROZEN is written, the cgroup,
+ if not already freezing, enters FREEZING state along with all its
+ descendant cgroups.
+ If THAWED is written, the self-state of the cgroup is changed to
+ THAWED. Note that the effective state may not change to THAWED if
+ the parent-state is still freezing. If a cgroup's effective state
+ becomes THAWED, all its descendants which are freezing because of
+ the cgroup also leave the freezing state.
+* freezer.self_freezing: Read only.
+ Shows the self-state. 0 if the self-state is THAWED; otherwise, 1.
+ This value is 1 iff the last write to freezer.state was "FROZEN".
+* freezer.parent_freezing: Read only.
+ Shows the parent-state. 0 if none of the cgroup's ancestors is
+ frozen; otherwise, 1.
+The root cgroup is non-freezable and the above interface files don't
* Examples of usage :
@@ -85,18 +121,3 @@ to unfreeze all tasks in the container :
This is the basic mechanism which should do the right thing for user space task
in a simple scenario.
-It's important to note that freezing can be incomplete. In that case we return
-EBUSY. This means that some tasks in the cgroup are busy doing something that
-prevents us from completely freezing the cgroup at this time. After EBUSY,
-the cgroup will remain partially frozen -- reflected by freezer.state reporting
-"FREEZING" when read. The state will remain "FREEZING" until one of these
- 1) Userspace cancels the freezing operation by writing "THAWED" to
- the freezer.state file
- 2) Userspace retries the freezing operation by writing "FROZEN" to
- the freezer.state file (writing "FREEZING" is not legal
- and returns EINVAL)
- 3) The tasks that blocked the cgroup from entering the "FROZEN"
- state disappear from the cgroup's set of tasks.
diff --git a/Documentation/cgroups/hugetlb.txt b/Documentation/cgroups/hugetlb.txt
new file mode 100644
@@ -0,0 +1,45 @@
+The HugeTLB controller allows to limit the HugeTLB usage per control group and
+enforces the controller limit during page fault. Since HugeTLB doesn't
+support page reclaim, enforcing the limit at page fault time implies that,
+the application will get SIGBUS signal if it tries to access HugeTLB pages
+beyond its limit. This requires the application to know beforehand how much
+HugeTLB pages it would require for its use.
+HugeTLB controller can be created by first mounting the cgroup filesystem.
+# mount -t cgroup -o hugetlb none /sys/fs/cgroup
+With the above step, the initial or the parent HugeTLB group becomes
+visible at /sys/fs/cgroup. At bootup, this group includes all the tasks in
+the system. /sys/fs/cgroup/tasks lists the tasks in this cgroup.
+New groups can be created under the parent group /sys/fs/cgroup.
+# cd /sys/fs/cgroup
+# mkdir g1
+# echo $$ > g1/tasks
+The above steps create a new group g1 and move the current shell
+process (bash) into it.
+Brief summary of control files
+ hugetlb.<hugepagesize>.limit_in_bytes # set/show limit of "hugepagesize" hugetlb usage
+ hugetlb.<hugepagesize>.max_usage_in_bytes # show max "hugepagesize" hugetlb usage recorded
+ hugetlb.<hugepagesize>.usage_in_bytes # show current res_counter usage for "hugepagesize" hugetlb
+ hugetlb.<hugepagesize>.failcnt # show the number of allocation failure due to HugeTLB limit
+For a system supporting two hugepage size (16M and 16G) the control
diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index dd88540bb99..8b8c28b9864 100644
@@ -18,16 +18,16 @@ from the rest of the system. The article on LWN  mentions some probable
uses of the memory controller. The memory controller can be used to
a. Isolate an application or a group of applications
- Memory hungry applications can be isolated and limited to a smaller
+ Memory-hungry applications can be isolated and limited to a smaller
amount of memory.
-b. Create a cgroup with limited amount of memory, this can be used
+b. Create a cgroup with a limited amount of memory; this can be used
as a good alternative to booting with mem=XXXX.
c. Virtualization solutions can control the amount of memory they want
to assign to a virtual machine instance.
d. A CD/DVD burner could control the amount of memory used by the
rest of the system to ensure that burning does not fail due to lack
of available memory.
-e. There are several other use cases, find one or use the controller just
+e. There are several other use cases; find one or use the controller just
for fun (to learn and hack on the VM subsystem).
Current Status: linux-2.6.34-mmotm(development version of 2010/April)
@@ -38,12 +38,12 @@ Features:
- optionally, memory+swap usage can be accounted and limited.
- hierarchical accounting
- soft limit
- - moving(recharging) account at moving a task is selectable.
+ - moving (recharging) account at moving a task is selectable.
- usage threshold notifier
- oom-killer disable knob and oom-notifier
- Root cgroup has no limit controls.
- Kernel memory support is work in progress, and the current version provides
+ Kernel memory support is a work in progress, and the current version provides
basically functionality. (See Section 2.7)
Brief summary of control files.
@@ -71,8 +71,15 @@ Brief summary of control files.
memory.oom_control # set/show oom controls.
memory.numa_stat # show the number of memory usage per numa node
+ memory.kmem.limit_in_bytes # set/show hard limit for kernel memory
+ memory.kmem.usage_in_bytes # show current kernel memory allocation
+ memory.kmem.failcnt # show the number of kernel memory usage hits limits
+ memory.kmem.max_usage_in_bytes # show max kernel memory usage recorded
memory.kmem.tcp.limit_in_bytes # set/show hard limit for tcp buf memory
memory.kmem.tcp.usage_in_bytes # show current tcp buf memory allocation
+ memory.kmem.tcp.failcnt # show the number of tcp buf memory usage hits limits
+ memory.kmem.tcp.max_usage_in_bytes # show max tcp buf memory usage recorded
@@ -142,9 +149,9 @@ Figure 1 shows the important aspects of the controller
3. Each page has a pointer to the page_cgroup, which in turn knows the
cgroup it belongs to
-The accounting is done as follows: mem_cgroup_charge() is invoked to setup
-the necessary data structures and check if the cgroup that is being charged
-is over its limit. If it is then reclaim is invoked on the cgroup.
+The accounting is done as follows: mem_cgroup_charge_common() is invoked to
+set up the necessary data structures and check if the cgroup that is being
+charged is over its limit. If it is, then reclaim is invoked on the cgroup.
More details can be found in the reclaim section of this document.
If everything goes well, a page meta-data-structure called page_cgroup is
updated. page_cgroup has its own LRU on cgroup.
@@ -161,13 +168,13 @@ for earlier. A file page will be accounted for as Page Cache when it's
inserted into inode (radix-tree). While it's mapped into the page tables of
processes, duplicate accounting is carefully avoided.
-A RSS page is unaccounted when it's fully unmapped. A PageCache page is
+An RSS page is unaccounted when it's fully unmapped. A PageCache page is
unaccounted when it's removed from radix-tree. Even if RSS pages are fully
unmapped (by kswapd), they may exist as SwapCache in the system until they
-are really freed. Such SwapCaches also also accounted.
+are really freed. Such SwapCaches are also accounted.
A swapped-in page is not accounted until it's mapped.
-Note: The kernel does swapin-readahead and read multiple swaps at once.
+Note: The kernel does swapin-readahead and reads multiple swaps at once.
This means swapped-in pages may contain pages for other tasks than a task
causing page fault. So, we avoid accounting at swap-in I/O.
@@ -187,12 +194,12 @@ the cgroup that brought it in -- this will happen on memory pressure).
But see section 8.2: when moving a task to another cgroup, its pages may
be recharged to the new cgroup, if move_charge_at_immigrate has been chosen.
-Exception: If CONFIG_CGROUP_CGROUP_MEM_RES_CTLR_SWAP is not used.
+Exception: If CONFIG_CGROUP_CGROUP_MEMCG_SWAP is not used.
When you do swapoff and make swapped-out pages of shmem(tmpfs) to
be backed into memory in force, charges for pages are accounted against the
caller of swapoff rather than the users of shmem.
-2.4 Swap Extension (CONFIG_CGROUP_MEM_RES_CTLR_SWAP)
+2.4 Swap Extension (CONFIG_MEMCG_SWAP)
Swap Extension allows you to record charge for swap. A swapped-in page is
charged back to original page allocator if possible.
@@ -207,7 +214,7 @@ memsw.limit_in_bytes.
Example: Assume a system with 4G of swap. A task which allocates 6G of memory
(by mistake) under 2G memory limitation will use all swap.
In this case, setting memsw.limit_in_bytes=3G will prevent bad use of swap.
-By using memsw limit, you can avoid system OOM which can be caused by swap
+By using the memsw limit, you can avoid system OOM which can be caused by swap
* why 'memory+swap' rather than swap.
@@ -215,7 +222,7 @@ The global LRU(kswapd) can swap out arbitrary pages. Swap-out means
to move account from memory to swap...there is no change in usage of
memory+swap. In other words, when we want to limit the usage of swap without
affecting global LRU, memory+swap limit is better than just limiting swap from
-OS point of view.
+an OS point of view.
* What happens when a cgroup hits memory.memsw.limit_in_bytes
When a cgroup hits memory.memsw.limit_in_bytes, it's useless to do swap-out
@@ -234,7 +241,7 @@ an OOM routine is invoked to select and kill the bulkiest task in the
cgroup. (See 10. OOM Control below.)
The reclaim algorithm has not been modified for cgroups, except that
-pages that are selected for reclaiming come from the per cgroup LRU
+pages that are selected for reclaiming come from the per-cgroup LRU
NOTE: Reclaim does not work for the root cgroup, since we cannot set any
@@ -259,35 +266,89 @@ When oom event notifier is registered, event will be delivered.
per-zone-per-cgroup LRU (cgroup's private LRU) is just guarded by
zone->lru_lock, it has no lock of its own.
-2.7 Kernel Memory Extension (CONFIG_CGROUP_MEM_RES_CTLR_KMEM)
+2.7 Kernel Memory Extension (CONFIG_MEMCG_KMEM)
With the Kernel memory extension, the Memory Controller is able to limit
the amount of kernel memory used by the system. Kernel memory is fundamentally
different than user memory, since it can't be swapped out, which makes it
possible to DoS the system by consuming too much of this precious resource.
+Kernel memory won't be accounted at all until limit on a group is set. This
+allows for existing setups to continue working without disruption. The limit
+cannot be set if the cgroup have children, or if there are already tasks in the
+cgroup. Attempting to set the limit under those conditions will return -EBUSY.
+When use_hierarchy == 1 and a group is accounted, its children will
+automatically be accounted regardless of their limit value.
+After a group is first limited, it will be kept being accounted until it
+is removed. The memory limitation itself, can of course be removed by writing
+-1 to memory.kmem.limit_in_bytes. In this case, kmem will be accounted, but not
Kernel memory limits are not imposed for the root cgroup. Usage for the root
-cgroup may or may not be accounted.
+cgroup may or may not be accounted. The memory used is accumulated into
+memory.kmem.usage_in_bytes, or in a separate counter when it makes sense.
+(currently only for tcp).
+The main "kmem" counter is fed into the main counter, so kmem charges will
+also be visible from the user counter.
Currently no soft limit is implemented for kernel memory. It is future work
to trigger slab reclaim when those limits are reached.
2.7.1 Current Kernel Memory resources accounted
+* stack pages: every process consumes some stack pages. By accounting into
+kernel memory, we prevent new processes from being created when the kernel
+memory usage is too high.
+* slab pages: pages allocated by the SLAB or SLUB allocator are tracked. A copy
+of each kmem_cache is created everytime the cache is touched by the first time
+from inside the memcg. The creation is done lazily, so some objects can still be
+skipped while the cache is being created. All objects in a slab page should
+belong to the same memcg. This only fails to hold when a task is migrated to a
+different memcg during the page allocation by the cache.
* sockets memory pressure: some sockets protocols have memory pressure
thresholds. The Memory Controller allows them to be controlled individually
per cgroup, instead of globally.
* tcp memory pressure: sockets memory pressure for the tcp protocol.
+2.7.3 Common use cases
+Because the "kmem" counter is fed to the main user counter, kernel memory can
+never be limited completely independently of user memory. Say "U" is the user
+limit, and "K" the kernel limit. There are three possible ways limits can be
+ U != 0, K = unlimited:
+ This is the standard memcg limitation mechanism already present before kmem
+ accounting. Kernel memory is completely ignored.
+ U != 0, K < U:
+ Kernel memory is a subset of the user memory. This setup is useful in
+ deployments where the total amount of memory per-cgroup is overcommited.
+ Overcommiting kernel memory limits is definitely not recommended, since the
+ box can still run out of non-reclaimable memory.
+ In this case, the admin could set up K so that the sum of all groups is
+ never greater than the total memory, and freely set U at the cost of his
+ U != 0, K >= U:
+ Since kmem charges will also be fed to the user counter and reclaim will be
+ triggered for the cgroup for both kinds of memory. This setup gives the
+ admin a unified view of memory, and it is also useful for people who just
+ want to track kernel memory usage.
3. User Interface
a. Enable CONFIG_CGROUPS
b. Enable CONFIG_RESOURCE_COUNTERS
-c. Enable CONFIG_CGROUP_MEM_RES_CTLR
-d. Enable CONFIG_CGROUP_MEM_RES_CTLR_SWAP (to use swap extension)
+c. Enable CONFIG_MEMCG
+d. Enable CONFIG_MEMCG_SWAP (to use swap extension)
+d. Enable CONFIG_MEMCG_KMEM (to use kmem extension)
1. Prepare the cgroups (see cgroups.txt, Why are cgroups needed?)
# mount -t tmpfs none /sys/fs/cgroup
@@ -314,7 +375,7 @@ We can check the usage:
# cat /sys/fs/cgroup/memory/0/memory.usage_in_bytes
-A successful write to this file does not guarantee a successful set of
+A successful write to this file does not guarantee a successful setting of
this limit to the value written into the file. This can be due to a
number of factors, such as rounding up to page boundaries or the total
availability of memory on the system. The user is required to re-read
@@ -348,7 +409,7 @@ Trying usual test under memory controller is always helpful.
Sometimes a user might find that the application under a cgroup is
-terminated by OOM killer. There are several causes for this:
+terminated by the OOM killer. There are several causes for this:
1. The cgroup limit is too low (just too low to do anything useful)
2. The user is using anonymous memory and swap is turned off or too low
@@ -356,7 +417,7 @@ terminated by OOM killer. There are several causes for this:
A sync followed by echo 1 > /proc/sys/vm/drop_caches will help get rid of
some of the pages cached in the cgroup (page cache pages).
-To know what happens, disable OOM_Kill by 10. OOM Control(see below) and
+To know what happens, disabling OOM_Kill as per "10. OOM Control" (below) and
seeing what happens will be helpful.
4.2 Task migration
@@ -397,13 +458,18 @@ About use_hierarchy, see Section 6.
Almost all pages tracked by this memory cgroup will be unmapped and freed.
Some pages cannot be freed because they are locked or in-use. Such pages are
- moved to parent(if use_hierarchy==1) or root (if use_hierarchy==0) and this
+ moved to parent (if use_hierarchy==1) or root (if use_hierarchy==0) and this
cgroup will be empty.
- Typical use case of this interface is that calling this before rmdir().
+ The typical use case for this interface is before calling rmdir().
Because rmdir() moves all pages to parent, some out-of-use page caches can be
moved to the parent. If you want to avoid that, force_empty will be useful.
+ Also, note that when memory.kmem.limit_in_bytes is set the charges due to
+ kernel pages will still be seen. This is not considered a failure and the
+ write will still return success. In this case, it is expected that
+ memory.kmem.usage_in_bytes == memory.usage_in_bytes.
About use_hierarchy, see Section 6.
5.2 stat file
@@ -464,6 +530,10 @@ Note:
Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of groups only.
+Please note that unlike the global swappiness, memcg knob set to 0
+really prevents from any swapping even if there is a swap storage
+available. This might lead to memcg OOM killer if there are no file
+pages to reclaim.
Following cgroups' swappiness can't be changed.
- root cgroup (uses /proc/sys/vm/swappiness).
@@ -484,7 +554,7 @@ You can reset failcnt by writing 0 to failcnt file.
For efficiency, as other kernel components, memory cgroup uses some optimization
to avoid unnecessary cacheline false sharing. usage_in_bytes is affected by the
-method and doesn't show 'exact' value of memory(and swap) usage, it's an fuzz
+method and doesn't show 'exact' value of memory (and swap) usage, it's a fuzz
value for efficient access. (Of course, when necessary, it's synchronized.)
If you want to know more exact memory usage, you should use RSS+CACHE(+SWAP)
value in memory.stat(see 5.2).
@@ -494,8 +564,8 @@ value in memory.stat(see 5.2).
This is similar to numa_maps but operates on a per-memcg basis. This is
useful for providing visibility into the numa locality information within
an memcg since the pages are allowed to be allocated from any physical
-node. One of the usecases is evaluating application performance by
-combining this information with the application's cpu allocation.
+node. One of the use cases is evaluating application performance by
+combining this information with the application's CPU allocation.
We export "total", "file", "anon" and "unevictable" pages per-node for
each memcg. The ouput format of memory.numa_stat is:
@@ -559,10 +629,10 @@ are pushed back to their soft limits. If the soft limit of each control
group is very high, they are pushed back as much as possible to make
sure that one control group does not starve the others of memory.
-Please note that soft limits is a best effort feature, it comes with
+Please note that soft limits is a best-effort feature; it comes with
no guarantees, but it does its best to make sure that when memory is
heavily contended for, memory is allocated based on the soft limit
-hints/setup. Currently soft limit based reclaim is setup such that
+hints/setup. Currently soft limit based reclaim is set up such that
it gets invoked from balance_pgdat (kswapd).
@@ -590,7 +660,7 @@ page tables.
-This feature is disabled by default. It can be enabled(and disabled again) by
+This feature is disabled by default. It can be enabledi (and disabled again) by
writing to memory.move_charge_at_immigrate of the destination cgroup.
If you want to enable it:
@@ -599,8 +669,8 @@ If you want to enable it:
Note: Each bits of move_charge_at_immigrate has its own meaning about what type
of charges should be moved. See 8.2 for details.
-Note: Charges are moved only when you move mm->owner, IOW, a leader of a thread
+Note: Charges are moved only when you move mm->owner, in other words,
+ a leader of a thread group.
Note: If we cannot find enough space for the task in the destination cgroup, we
try to make space by reclaiming memory. Task migration may fail if we
cannot make enough space.
@@ -610,25 +680,25 @@ And if you want disable it again:
# echo 0 > memory.move_charge_at_immigrate
-8.2 Type of charges which can be move
+8.2 Type of charges which can be moved
-Each bits of move_charge_at_immigrate has its own meaning about what type of
-charges should be moved. But in any cases, it must be noted that an account of
-a page or a swap can be moved only when it is charged to the task's current(old)
+Each bit in move_charge_at_immigrate has its own meaning about what type of
+charges should be moved. But in any case, it must be noted that an account of
+a page or a swap can be moved only when it is charged to the task's current
+(old) memory cgroup.
bit | what type of charges would be moved ?
- 0 | A charge of an anonymous page(or swap of it) used by the target task.
- | You must enable Swap Extension(see 2.4) to enable move of swap charges.
+ 0 | A charge of an anonymous page (or swap of it) used by the target task.
+ | You must enable Swap Extension (see 2.4) to enable move of swap charges.
- 1 | A charge of file pages(normal file, tmpfs file(e.g. ipc shared memory)
+ 1 | A charge of file pages (normal file, tmpfs file (e.g. ipc shared memory)
| and swaps of tmpfs file) mmapped by the target task. Unlike the case of
- | anonymous pages, file pages(and swaps) in the range mmapped by the task
+ | anonymous pages, file pages (and swaps) in the range mmapped by the task
| will be moved even if the task hasn't done page fault, i.e. they might
| not be the task's "RSS", but other task's "RSS" that maps the same file.
- | And mapcount of the page is ignored(the page can be moved even if
- | page_mapcount(page) > 1). You must enable Swap Extension(see 2.4) to
+ | And mapcount of the page is ignored (the page can be moved even if
+ | page_mapcount(page) > 1). You must enable Swap Extension (see 2.4) to
| enable move of swap charges.
@@ -638,11 +708,11 @@ memory cgroup.
9. Memory thresholds
-Memory cgroup implements memory thresholds using cgroups notification
+Memory cgroup implements memory thresholds using the cgroups notification
API (see cgroups.txt). It allows to register multiple memory and memsw
thresholds and gets notifications when it crosses.
-To register a threshold application need:
+To register a threshold, an application must:
- create an eventfd using eventfd(2);
- open memory.usage_in_bytes or memory.memsw.usage_in_bytes;
- write string like "<event_fd> <fd of memory.usage_in_bytes> <threshold>" to
@@ -657,24 +727,24 @@ It's applicable for root and non-root cgroup.
memory.oom_control file is for OOM notification and other controls.
-Memory cgroup implements OOM notifier using cgroup notification
+Memory cgroup implements OOM notifier using the cgroup notification
API (See cgroups.txt). It allows to register multiple OOM notification
delivery and gets notification when OOM happens.
-To register a notifier, application need:
+To register a notifier, an application must:
- create an eventfd using eventfd(2)
- open memory.oom_control file
- write string like "<event_fd> <fd of memory.oom_control>" to
-Application will be notified through eventfd when OOM happens.
-OOM notification doesn't work for root cgroup.
+The application will be notified through eventfd when OOM happens.
+OOM notification doesn't work for the root cgroup.
-You can disable OOM-killer by writing "1" to memory.oom_control file, as:
+You can disable the OOM-killer by writing "1" to memory.oom_control file, as:
#echo 1 > memory.oom_control
-This operation is only allowed to the top cgroup of sub-hierarchy.
+This operation is only allowed to the top cgroup of a sub-hierarchy.
If OOM-killer is disabled, tasks under cgroup will hang/sleep
in memory cgroup's OOM-waitqueue when they request accountable memory.
diff --git a/Documentation/cgroups/net_prio.txt b/Documentation/cgroups/net_prio.txt
index 01b32263559..a82cbd28ea8 100644
@@ -51,3 +51,5 @@ One usage for the net_prio cgroup is with mqprio qdisc allowing application
traffic to be steered to hardware/driver based traffic classes. These mappings
can then be managed by administrators or other networking protocols such as
+A new net_prio cgroup inherits the parent's configuration.
diff --git a/Documentation/cgroups/resource_counter.txt b/Documentation/cgroups/resource_counter.txt
index 0c4a344e78f..c4d99ed0b41 100644
@@ -83,16 +83,17 @@ to work with it.
res_counter->lock internally (it must be called with res_counter->lock
held). The force parameter indicates whether we can bypass the limit.
- e. void res_counter_uncharge[_locked]
+ e. u64 res_counter_uncharge[_locked]
(struct res_counter *rc, unsigned long val)
When a resource is released (freed) it should be de-accounted
from the resource counter it was accounted to. This is called
+ "uncharging". The return value of this function indicate the amount
+ of charges still present in the counter.
The _locked routines imply that the res_counter->lock is taken.
- f. void res_counter_uncharge_until
+ f. u64 res_counter_uncharge_until
(struct res_counter *rc, struct res_counter *top,
unsinged long val)