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-rw-r--r--Documentation/admin-guide/cgroup-v1/cpusets.rst11
-rw-r--r--kernel/cgroup/cpuset.c8
2 files changed, 17 insertions, 2 deletions
diff --git a/Documentation/admin-guide/cgroup-v1/cpusets.rst b/Documentation/admin-guide/cgroup-v1/cpusets.rst
index 86a6ae995d54..7ade3abd342a 100644
--- a/Documentation/admin-guide/cgroup-v1/cpusets.rst
+++ b/Documentation/admin-guide/cgroup-v1/cpusets.rst
@@ -223,6 +223,17 @@ cpu_online_mask using a CPU hotplug notifier, and the mems file
automatically tracks the value of node_states[N_MEMORY]--i.e.,
nodes with memory--using the cpuset_track_online_nodes() hook.
+The cpuset.effective_cpus and cpuset.effective_mems files are
+normally read-only copies of cpuset.cpus and cpuset.mems files
+respectively. If the cpuset cgroup filesystem is mounted with the
+special "cpuset_v2_mode" option, the behavior of these files will become
+similar to the corresponding files in cpuset v2. In other words, hotplug
+events will not change cpuset.cpus and cpuset.mems. Those events will
+only affect cpuset.effective_cpus and cpuset.effective_mems which show
+the actual cpus and memory nodes that are currently used by this cpuset.
+See Documentation/admin-guide/cgroup-v2.rst for more information about
+cpuset v2 behavior.
+
1.4 What are exclusive cpusets ?
--------------------------------
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 58f5073acff7..729d3a5c772e 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -358,8 +358,12 @@ static DECLARE_WORK(cpuset_hotplug_work, cpuset_hotplug_workfn);
static DECLARE_WAIT_QUEUE_HEAD(cpuset_attach_wq);
/*
- * Cgroup v2 behavior is used when on default hierarchy or the
- * cgroup_v2_mode flag is set.
+ * Cgroup v2 behavior is used on the "cpus" and "mems" control files when
+ * on default hierarchy or when the cpuset_v2_mode flag is set by mounting
+ * the v1 cpuset cgroup filesystem with the "cpuset_v2_mode" mount option.
+ * With v2 behavior, "cpus" and "mems" are always what the users have
+ * requested and won't be changed by hotplug events. Only the effective
+ * cpus or mems will be affected.
*/
static inline bool is_in_v2_mode(void)
{