cgroup/cpuset: Rebind/migrate mm only for threadgroup leader in cpuset_update_tasks_nodemask()

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As reported by sashiko [1], cpuset_update_tasks_nodemask() will do
mpol_rebind_mm() and possibly cpuset_migrate_mm() for all threads of
a multithreaded process. Since commit 3df9ca0a2b ("cpuset: migrate
memory only for threadgroup leaders"), cpuset_attach() had been updated
to rebind and migrate memory only for threadgroup leaders to mark the
group leader as the owner of the mm_struct.

To be consistent and avoid unnecessary performance overhead for heavily
multithreaded processes, follow the cpuset_attach() example and perform
memory rebind and migration only for threadgroup leaders.

Also add a paragraph in cgroup-v2.rst under cpuset.mems that the
threadgroup leader is the memory owner of that threadgroup. Therefore
the non-leading threads shouldn't be in other cgroups whose "cpuset.mems"
doesn't fully overlap that of the group leader.

[1] https://sashiko.dev/#/patchset/20260621032816.1806773-1-longman%40redhat.com

Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Ridong Chen <ridong.chen@linux.dev>
Signed-off-by: Tejun Heo <tj@kernel.org>

...

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Waiman Long 2026-06-23 19:04:13 -04:00 • committed by Tejun Heo

parent 866f587e9c

commit eda17a3a70

2 changed files with 11 additions and 0 deletions

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7

Documentation/admin-guide/cgroup-v2.rst

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4

kernel/cgroup/cpuset.c

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