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-rw-r--r--Documentation/cgroup-v2.txt73
1 files changed, 62 insertions, 11 deletions
diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index 94350d79e169..3b8449f8ac7e 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -47,8 +47,12 @@ CONTENTS
5-3. IO
5-3-1. IO Interface Files
5-3-2. Writeback
- 5-4. RDMA
- 5-4-1. RDMA Interface Files
+ 5-4. PID
+ 5-4-1. PID Interface Files
+ 5-5. RDMA
+ 5-5-1. RDMA Interface Files
+ 5-6. Misc
+ 5-6-1. perf_event
6. Namespace
6-1. Basics
6-2. The Root and Views
@@ -330,14 +334,12 @@ a process with a non-root euid to migrate a target process into a
cgroup by writing its PID to the "cgroup.procs" file, the following
conditions must be met.
-- The writer's euid must match either uid or suid of the target process.
-
- The writer must have write access to the "cgroup.procs" file.
- The writer must have write access to the "cgroup.procs" file of the
common ancestor of the source and destination cgroups.
-The above three constraints ensure that while a delegatee may migrate
+The above two constraints ensure that while a delegatee may migrate
processes around freely in the delegated sub-hierarchy it can't pull
in from or push out to outside the sub-hierarchy.
@@ -352,10 +354,10 @@ all processes under C0 and C1 belong to U0.
Let's also say U0 wants to write the PID of a process which is
currently in C10 into "C00/cgroup.procs". U0 has write access to the
-file and uid match on the process; however, the common ancestor of the
-source cgroup C10 and the destination cgroup C00 is above the points
-of delegation and U0 would not have write access to its "cgroup.procs"
-files and thus the write will be denied with -EACCES.
+file; however, the common ancestor of the source cgroup C10 and the
+destination cgroup C00 is above the points of delegation and U0 would
+not have write access to its "cgroup.procs" files and thus the write
+will be denied with -EACCES.
2-6. Guidelines
@@ -1121,12 +1123,51 @@ writeback as follows.
vm.dirty[_background]_ratio.
-5-4. RDMA
+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.
+
+
+5-5. RDMA
The "rdma" controller regulates the distribution and accounting of
of RDMA resources.
-5-4-1. RDMA Interface Files
+5-5-1. RDMA Interface Files
rdma.max
A readwrite nested-keyed file that exists for all the cgroups
@@ -1157,6 +1198,16 @@ of RDMA resources.
ocrdma1 hca_handle=1 hca_object=23
+5-6. Misc
+
+5-6-1. perf_event
+
+perf_event controller, if not mounted on a legacy hierarchy, is
+automatically enabled on the v2 hierarchy so that perf events can
+always be filtered by cgroup v2 path. The controller can still be
+moved to a legacy hierarchy after v2 hierarchy is populated.
+
+
6. Namespace
6-1. Basics