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cgroup: Add missing cgroup-v2 PID controller documentation.

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Signed-off-by: Hans Ragas <hansr@fb.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
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Hans Ragas 2017-01-10 17:42:34 +00:00 committed by Tejun Heo
parent 7b4632f048
commit 20c56e595c
1 changed files with 41 additions and 0 deletions
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Documentation/cgroup-v2.txt
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@ -47,6 +47,8 @@ CONTENTS
5-3. IO
5-3-1. IO Interface Files
5-3-2. Writeback
5-4. PID
5-4-1. PID Interface Files
6. Namespace
6-1. Basics
6-2. The Root and Views
@ -1119,6 +1121,45 @@ writeback as follows.
vm.dirty[_background]_ratio.
5-4. PID
The process number controller is used to allow a cgroup to stop any
new tasks from being fork()'d or clone()'d after a specified limit is
reached.
The number of tasks in a cgroup can be exhausted in ways which other
controllers cannot prevent, thus warranting its own controller. For
example, a fork bomb is likely to exhaust the number of tasks before
hitting memory restrictions.
Note that PIDs used in this controller refer to TIDs, process IDs as
used by the kernel.
5-4-1. PID Interface Files
pids.max
A read-write single value file which exists on non-root cgroups. The
default is "max".
Hard limit of number of processes.
pids.current
A read-only single value file which exists on all cgroups.
The number of processes currently in the cgroup and its descendants.
Organisational operations are not blocked by cgroup policies, so it is
possible to have pids.current > pids.max. This can be done by either
setting the limit to be smaller than pids.current, or attaching enough
processes to the cgroup such that pids.current is larger than
pids.max. However, it is not possible to violate a cgroup PID policy
through fork() or clone(). These will return -EAGAIN if the creation
of a new process would cause a cgroup policy to be violated.
6. Namespace
6-1. Basics