mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-12-02 08:34:20 +08:00
6255c46fa0
cgroup-legacy may be too loaded. Rename the docs so that they're postfixed with v1 and v2. * s/cgroup-legacy/cgroup-v1/ * s/cgroup.txt/cgroup-v2.txt/ Signed-off-by: Tejun Heo <tj@kernel.org>
86 lines
3.0 KiB
Plaintext
86 lines
3.0 KiB
Plaintext
Process Number Controller
|
|
=========================
|
|
|
|
Abstract
|
|
--------
|
|
|
|
The process number controller is used to allow a cgroup hierarchy to stop any
|
|
new tasks from being fork()'d or clone()'d after a certain limit is reached.
|
|
|
|
Since it is trivial to hit the task limit without hitting any kmemcg limits in
|
|
place, PIDs are a fundamental resource. As such, PID exhaustion must be
|
|
preventable in the scope of a cgroup hierarchy by allowing resource limiting of
|
|
the number of tasks in a cgroup.
|
|
|
|
Usage
|
|
-----
|
|
|
|
In order to use the `pids` controller, set the maximum number of tasks in
|
|
pids.max (this is not available in the root cgroup for obvious reasons). The
|
|
number of processes currently in the cgroup is given by pids.current.
|
|
|
|
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 > pids.max. However, it is not possible to violate a cgroup
|
|
policy through fork() or clone(). fork() and clone() will return -EAGAIN if the
|
|
creation of a new process would cause a cgroup policy to be violated.
|
|
|
|
To set a cgroup to have no limit, set pids.max to "max". This is the default for
|
|
all new cgroups (N.B. that PID limits are hierarchical, so the most stringent
|
|
limit in the hierarchy is followed).
|
|
|
|
pids.current tracks all child cgroup hierarchies, so parent/pids.current is a
|
|
superset of parent/child/pids.current.
|
|
|
|
Example
|
|
-------
|
|
|
|
First, we mount the pids controller:
|
|
# mkdir -p /sys/fs/cgroup/pids
|
|
# mount -t cgroup -o pids none /sys/fs/cgroup/pids
|
|
|
|
Then we create a hierarchy, set limits and attach processes to it:
|
|
# mkdir -p /sys/fs/cgroup/pids/parent/child
|
|
# echo 2 > /sys/fs/cgroup/pids/parent/pids.max
|
|
# echo $$ > /sys/fs/cgroup/pids/parent/cgroup.procs
|
|
# cat /sys/fs/cgroup/pids/parent/pids.current
|
|
2
|
|
#
|
|
|
|
It should be noted that attempts to overcome the set limit (2 in this case) will
|
|
fail:
|
|
|
|
# cat /sys/fs/cgroup/pids/parent/pids.current
|
|
2
|
|
# ( /bin/echo "Here's some processes for you." | cat )
|
|
sh: fork: Resource temporary unavailable
|
|
#
|
|
|
|
Even if we migrate to a child cgroup (which doesn't have a set limit), we will
|
|
not be able to overcome the most stringent limit in the hierarchy (in this case,
|
|
parent's):
|
|
|
|
# echo $$ > /sys/fs/cgroup/pids/parent/child/cgroup.procs
|
|
# cat /sys/fs/cgroup/pids/parent/pids.current
|
|
2
|
|
# cat /sys/fs/cgroup/pids/parent/child/pids.current
|
|
2
|
|
# cat /sys/fs/cgroup/pids/parent/child/pids.max
|
|
max
|
|
# ( /bin/echo "Here's some processes for you." | cat )
|
|
sh: fork: Resource temporary unavailable
|
|
#
|
|
|
|
We can set a limit that is smaller than pids.current, which will stop any new
|
|
processes from being forked at all (note that the shell itself counts towards
|
|
pids.current):
|
|
|
|
# echo 1 > /sys/fs/cgroup/pids/parent/pids.max
|
|
# /bin/echo "We can't even spawn a single process now."
|
|
sh: fork: Resource temporary unavailable
|
|
# echo 0 > /sys/fs/cgroup/pids/parent/pids.max
|
|
# /bin/echo "We can't even spawn a single process now."
|
|
sh: fork: Resource temporary unavailable
|
|
#
|