cgroup: trivial fixes for Documentation/cgroups/cgroups.txt
While reading through Documentation/cgroups/cgroups.txt, I found a number of minor wordos and typos. The patch below is a conservative handling of some of these: it provides just a number of "obviously correct" fixes to the English that improve the readability of the document somewhat. Obviously some more significant fixes could be made to the document, but some of those may not be in the "obviously correct" category. Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com> Signed-off-by: Tejun Heo <tj@kernel.org>
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Michael Kerrisk
Tejun Heo
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commit
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@ -63,9 +63,9 @@ an instance of the cgroup virtual filesystem associated with it.
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At any one time there may be multiple active hierarchies of task
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cgroups. Each hierarchy is a partition of all tasks in the system.
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User level code may create and destroy cgroups by name in an
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User-level code may create and destroy cgroups by name in an
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instance of the cgroup virtual file system, specify and query to
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which cgroup a task is assigned, and list the task pids assigned to
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which cgroup a task is assigned, and list the task PIDs assigned to
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a cgroup. Those creations and assignments only affect the hierarchy
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associated with that instance of the cgroup file system.
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@ -73,7 +73,7 @@ On their own, the only use for cgroups is for simple job
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tracking. The intention is that other subsystems hook into the generic
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cgroup support to provide new attributes for cgroups, such as
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accounting/limiting the resources which processes in a cgroup can
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access. For example, cpusets (see Documentation/cgroups/cpusets.txt) allows
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access. For example, cpusets (see Documentation/cgroups/cpusets.txt) allow
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you to associate a set of CPUs and a set of memory nodes with the
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tasks in each cgroup.
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@ -81,11 +81,11 @@ tasks in each cgroup.
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----------------------------
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There are multiple efforts to provide process aggregations in the
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Linux kernel, mainly for resource tracking purposes. Such efforts
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Linux kernel, mainly for resource-tracking purposes. Such efforts
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include cpusets, CKRM/ResGroups, UserBeanCounters, and virtual server
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namespaces. These all require the basic notion of a
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grouping/partitioning of processes, with newly forked processes ending
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in the same group (cgroup) as their parent process.
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up in the same group (cgroup) as their parent process.
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The kernel cgroup patch provides the minimum essential kernel
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mechanisms required to efficiently implement such groups. It has
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@ -128,14 +128,14 @@ following lines:
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/ \
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Professors (15%) students (5%)
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Browsers like Firefox/Lynx go into the WWW network class, while (k)nfsd go
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into NFS network class.
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Browsers like Firefox/Lynx go into the WWW network class, while (k)nfsd goes
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into the NFS network class.
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At the same time Firefox/Lynx will share an appropriate CPU/Memory class
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depending on who launched it (prof/student).
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With the ability to classify tasks differently for different resources
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(by putting those resource subsystems in different hierarchies) then
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(by putting those resource subsystems in different hierarchies),
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the admin can easily set up a script which receives exec notifications
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and depending on who is launching the browser he can
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@ -146,19 +146,19 @@ a separate cgroup for every browser launched and associate it with
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appropriate network and other resource class. This may lead to
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proliferation of such cgroups.
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Also lets say that the administrator would like to give enhanced network
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Also let's say that the administrator would like to give enhanced network
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access temporarily to a student's browser (since it is night and the user
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wants to do online gaming :)) OR give one of the students simulation
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apps enhanced CPU power,
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wants to do online gaming :)) OR give one of the student's simulation
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apps enhanced CPU power.
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With ability to write pids directly to resource classes, it's just a
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With ability to write PIDs directly to resource classes, it's just a
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matter of:
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# echo pid > /sys/fs/cgroup/network/<new_class>/tasks
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(after some time)
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# echo pid > /sys/fs/cgroup/network/<orig_class>/tasks
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Without this ability, he would have to split the cgroup into
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Without this ability, the administrator would have to split the cgroup into
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multiple separate ones and then associate the new cgroups with the
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new resource classes.
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@ -188,17 +188,17 @@ Control Groups extends the kernel as follows:
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- A cgroup hierarchy filesystem can be mounted for browsing and
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manipulation from user space.
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- You can list all the tasks (by pid) attached to any cgroup.
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- You can list all the tasks (by PID) attached to any cgroup.
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The implementation of cgroups requires a few, simple hooks
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into the rest of the kernel, none in performance critical paths:
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into the rest of the kernel, none in performance-critical paths:
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- in init/main.c, to initialize the root cgroups and initial
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css_set at system boot.
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- in fork and exit, to attach and detach a task from its css_set.
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In addition a new file system, of type "cgroup" may be mounted, to
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In addition, a new file system of type "cgroup" may be mounted, to
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enable browsing and modifying the cgroups presently known to the
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kernel. When mounting a cgroup hierarchy, you may specify a
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comma-separated list of subsystems to mount as the filesystem mount
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@ -231,13 +231,13 @@ as the path relative to the root of the cgroup file system.
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Each cgroup is represented by a directory in the cgroup file system
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containing the following files describing that cgroup:
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- tasks: list of tasks (by pid) attached to that cgroup. This list
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is not guaranteed to be sorted. Writing a thread id into this file
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- tasks: list of tasks (by PID) attached to that cgroup. This list
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is not guaranteed to be sorted. Writing a thread ID into this file
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moves the thread into this cgroup.
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- cgroup.procs: list of tgids in the cgroup. This list is not
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guaranteed to be sorted or free of duplicate tgids, and userspace
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- cgroup.procs: list of thread group IDs in the cgroup. This list is
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not guaranteed to be sorted or free of duplicate TGIDs, and userspace
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should sort/uniquify the list if this property is required.
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Writing a thread group id into this file moves all threads in that
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Writing a thread group ID into this file moves all threads in that
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group into this cgroup.
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- notify_on_release flag: run the release agent on exit?
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- release_agent: the path to use for release notifications (this file
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@ -262,7 +262,7 @@ cgroup file system directories.
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When a task is moved from one cgroup to another, it gets a new
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css_set pointer - if there's an already existing css_set with the
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desired collection of cgroups then that group is reused, else a new
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desired collection of cgroups then that group is reused, otherwise a new
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css_set is allocated. The appropriate existing css_set is located by
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looking into a hash table.
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@ -293,7 +293,7 @@ file system) of the abandoned cgroup. This enables automatic
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removal of abandoned cgroups. The default value of
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notify_on_release in the root cgroup at system boot is disabled
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(0). The default value of other cgroups at creation is the current
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value of their parents notify_on_release setting. The default value of
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value of their parents' notify_on_release settings. The default value of
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a cgroup hierarchy's release_agent path is empty.
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1.5 What does clone_children do ?
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@ -317,7 +317,7 @@ the "cpuset" cgroup subsystem, the steps are something like:
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4) Create the new cgroup by doing mkdir's and write's (or echo's) in
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the /sys/fs/cgroup virtual file system.
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5) Start a task that will be the "founding father" of the new job.
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6) Attach that task to the new cgroup by writing its pid to the
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6) Attach that task to the new cgroup by writing its PID to the
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/sys/fs/cgroup/cpuset/tasks file for that cgroup.
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7) fork, exec or clone the job tasks from this founding father task.
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@ -345,7 +345,7 @@ and then start a subshell 'sh' in that cgroup:
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2.1 Basic Usage
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---------------
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Creating, modifying, using the cgroups can be done through the cgroup
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Creating, modifying, using cgroups can be done through the cgroup
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virtual filesystem.
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To mount a cgroup hierarchy with all available subsystems, type:
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@ -442,7 +442,7 @@ You can attach the current shell task by echoing 0:
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# echo 0 > tasks
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You can use the cgroup.procs file instead of the tasks file to move all
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threads in a threadgroup at once. Echoing the pid of any task in a
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threads in a threadgroup at once. Echoing the PID of any task in a
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threadgroup to cgroup.procs causes all tasks in that threadgroup to be
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be attached to the cgroup. Writing 0 to cgroup.procs moves all tasks
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in the writing task's threadgroup.
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@ -480,7 +480,7 @@ in /proc/mounts and /proc/<pid>/cgroups.
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There is mechanism which allows to get notifications about changing
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status of a cgroup.
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To register new notification handler you need:
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To register a new notification handler you need to:
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- create a file descriptor for event notification using eventfd(2);
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- open a control file to be monitored (e.g. memory.usage_in_bytes);
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- write "<event_fd> <control_fd> <args>" to cgroup.event_control.
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@ -489,7 +489,7 @@ To register new notification handler you need:
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eventfd will be woken up by control file implementation or when the
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cgroup is removed.
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To unregister notification handler just close eventfd.
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To unregister a notification handler just close eventfd.
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NOTE: Support of notifications should be implemented for the control
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file. See documentation for the subsystem.
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@ -503,7 +503,7 @@ file. See documentation for the subsystem.
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Each kernel subsystem that wants to hook into the generic cgroup
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system needs to create a cgroup_subsys object. This contains
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various methods, which are callbacks from the cgroup system, along
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with a subsystem id which will be assigned by the cgroup system.
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with a subsystem ID which will be assigned by the cgroup system.
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Other fields in the cgroup_subsys object include:
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@ -517,7 +517,7 @@ Other fields in the cgroup_subsys object include:
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at system boot.
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Each cgroup object created by the system has an array of pointers,
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indexed by subsystem id; this pointer is entirely managed by the
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indexed by subsystem ID; this pointer is entirely managed by the
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subsystem; the generic cgroup code will never touch this pointer.
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3.2 Synchronization
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@ -640,7 +640,7 @@ void post_clone(struct cgroup *cgrp)
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Called during cgroup_create() to do any parameter
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initialization which might be required before a task could attach. For
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example in cpusets, no task may attach before 'cpus' and 'mems' are set
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example, in cpusets, no task may attach before 'cpus' and 'mems' are set
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up.
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void bind(struct cgroup *root)
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@ -680,5 +680,5 @@ A: bash's builtin 'echo' command does not check calls to write() against
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Q: When I attach processes, only the first of the line gets really attached !
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A: We can only return one error code per call to write(). So you should also
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put only ONE pid.
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put only ONE PID.
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