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Subject[PATCH v3 02/12] cpuset: update cpuset->effective_{cpus,mems} at hotplug
We're going to have separate user-configured masks and effective ones.

Eventually configured masks can only be changed by writing cpuset.cpus
and cpuset.mems, and they won't be restricted by parent cpuset. While
effective masks reflect cpu/memory hotplug and hierachical restriction,
and these are the real masks that apply to the tasks in the cpuset.

We calculate effective mask this way:
- top cpuset's effective_mask == online_mask, otherwise
- cpuset's effective_mask == configured_mask & parent effective_mask,
if the result is empty, it inherits parent effective mask.

Those behavior changes are for default hierarchy only. For legacy
hierarchy, effective_mask and configured_mask are the same, so we won't
break old interfaces.

To make cs->effective_{cpus,mems} to be effective masks, we need to
- update the effective masks at hotplug
- update the effective masks at config change
- take on ancestor's mask when the effective mask is empty

The first item is done here.

This won't introduce behavior change.

Signed-off-by: Li Zefan <>
kernel/cpuset.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index ef0974c..94f651d 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2082,6 +2082,7 @@ retry:

cpumask_andnot(cs->cpus_allowed, cs->cpus_allowed, &off_cpus);
+ cpumask_andnot(cs->effective_cpus, cs->effective_cpus, &off_cpus);

@@ -2096,6 +2097,7 @@ retry:

nodes_andnot(cs->mems_allowed, cs->mems_allowed, off_mems);
+ nodes_andnot(cs->effective_mems, cs->effective_mems, off_mems);

@@ -2159,6 +2161,7 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
if (cpus_updated) {
cpumask_copy(top_cpuset.cpus_allowed, &new_cpus);
+ cpumask_copy(top_cpuset.effective_cpus, &new_cpus);
/* we don't mess with cpumasks of tasks in top_cpuset */
@@ -2167,6 +2170,7 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
if (mems_updated) {
top_cpuset.mems_allowed = new_mems;
+ top_cpuset.effective_mems = new_mems;

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