diff options
Diffstat (limited to 'Documentation/cgroups')
| -rw-r--r-- | Documentation/cgroups/cgroups.txt | 92 | ||||
| -rw-r--r-- | Documentation/cgroups/memory.txt | 90 |
2 files changed, 101 insertions, 81 deletions
diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt index 4a0b64c..9e04196c 100644 --- a/Documentation/cgroups/cgroups.txt +++ b/Documentation/cgroups/cgroups.txt @@ -29,7 +29,8 @@ CONTENTS: 3.1 Overview 3.2 Synchronization 3.3 Subsystem API -4. Questions +4. Extended attributes usage +5. Questions 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 +matter of: # 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 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 +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. @@ -292,7 +293,7 @@ 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 ? @@ -316,7 +317,7 @@ 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 +345,7 @@ 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 virtual filesystem. To mount a cgroup hierarchy with all available subsystems, type: @@ -441,7 +442,7 @@ 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. @@ -479,7 +480,7 @@ 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. @@ -488,7 +489,7 @@ 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. @@ -502,7 +503,7 @@ 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: @@ -516,7 +517,7 @@ 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 @@ -639,7 +640,7 @@ void post_clone(struct cgroup *cgrp) 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 +example, in cpusets, no task may attach before 'cpus' and 'mems' are set up. void bind(struct cgroup *root) @@ -650,7 +651,26 @@ 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' ? @@ -660,5 +680,5 @@ 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/memory.txt b/Documentation/cgroups/memory.txt index 4372e6b..c07f7b4 100644 --- a/Documentation/cgroups/memory.txt +++ b/Documentation/cgroups/memory.txt @@ -18,16 +18,16 @@ from the rest of the system. The article on LWN [12] 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. @@ -144,9 +144,9 @@ 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 accounting is done as follows: mem_cgroup_charge() 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. +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. @@ -163,13 +163,13 @@ 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. @@ -209,7 +209,7 @@ 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 shortage. * why 'memory+swap' rather than swap. @@ -217,7 +217,7 @@ 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 @@ -236,7 +236,7 @@ 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 list. NOTE: Reclaim does not work for the root cgroup, since we cannot set any @@ -316,7 +316,7 @@ We can check the usage: # cat /sys/fs/cgroup/memory/0/memory.usage_in_bytes 1216512 -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 @@ -350,7 +350,7 @@ Trying usual test under memory controller is always helpful. 4.1 Troubleshooting 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 @@ -358,7 +358,7 @@ 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 @@ -399,10 +399,10 @@ 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. @@ -486,7 +486,7 @@ 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). @@ -496,8 +496,8 @@ 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: @@ -561,10 +561,10 @@ 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). 7.1 Interface @@ -592,7 +592,7 @@ page tables. 8.1 Interface -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: @@ -601,8 +601,8 @@ 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 - group. +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. @@ -612,25 +612,25 @@ 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) -memory cgroup. +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. 8.3 TODO @@ -640,11 +640,11 @@ 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 @@ -659,24 +659,24 @@ 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 cgroup.event_control -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. |