Re: [PATCH 0/4] sched/numa: Add per-process automatic NUMA balancing control

[Li Zhe]

On 10/13/26 3:39 PM, Chen Yu wrote:
> On Tue, Sep 08, 2026 at 08:24:42PM +0800, Li Zhe wrote:
>> Automatic NUMA balancing is controlled globally through the
>> kernel.numa_balancing sysctl and can be influenced indirectly through
>> memory policy. That works well as a system default, but it is too coarse
>> for workloads where a launcher wants most processes to use the default
>> policy while a selected process opts out because it already manages NUMA
>> placement or cannot afford the sampling overhead.
>>
>> A recent per-cgroup proposal tried to address this by adding a
>> cgroup-local enable knob plus a NUMA_BALANCING_CGROUP mode where
>> balancing was disabled by default and then enabled for selected cgroups
>> [1]. The discussion also noted that automatic NUMA balancing already
>> operates at task/process granularity, that the knob is not a resource
>> control attribute, and that task/process controls such as sched_setattr()
>> or prctl() may be a better fit while cgroups and cpusets continue to
>> describe workload grouping and placement domains.
>>
>> There is also prior art from 2023 prctl() proposals [2][3]. Those
>> versions used a per-mm mode with disabled/enabled/default states, added
>> NumaB_mode to /proc/<pid>/status, and changed the global static key
>> handling so a per-process enable could override the global sysctl.
>>
>> This series takes a more conservative variant to preserve existing
>> administrator and workload expectations. Keeping the global sysctl as a
>> hard off switch means an administrator can still disable all automatic
>> NUMA balancing activity with one knob. Using a weak two-state
>> per-process opt-out/allow ABI avoids exposing a "default" state whose
>> meaning depends on global policy and is therefore easy to misinterpret.
>> Storing the configured mode in signal_struct gives the control explicit
>> thread-group semantics and avoids making unrelated non-thread CLONE_VM
>> users share the policy merely because they share an mm.
>>
>> The series implements a per-process interface: a thread group may use
>> prctl() to set or get its configured automatic NUMA balancing mode. A
>> process can opt out of new periodic NUMA scan scheduling and NUMA
>> scheduler accounting, or opt back in. Existing hinting faults and queued
>> work are allowed to drain naturally as the disabled state takes effect.
>> When kernel.numa_balancing is 0, a process-local enable request does not
>> override it.
>>
>> A separate task_struct scheduler snapshot is used by enqueue/dequeue
>> accounting so the scheduler can consistently account the state that was
>> in effect when a task entered the runqueue. This avoids changing
>> historical task accounting while still allowing a process mode change to
>> take effect through the normal dequeue/update/enqueue path.
>>
>> The series also exposes the process NUMA balancing mode in
>> /proc/<pid>/status and documents the new prctl() ABI and its interaction
>> with the global sysctl.
>>
> Can the global key be extended to tri-state, like the THP settings?
> To keep it backward-compatible, echoing 0 and 1 remains the same effect.
> The user can also echo always, advise, or never to it.
> We have a similar proposal here for cache-aware scheduling[1]
> In this way, the user does not have to disable NUMA balancing one by one
> across the whole system.
>
> Yafang Shao has a bpf-cgroup based NUMA balancing proposal[2].
> Overall I support fine-grained control of NUMA balancing, and I'm curious
> what the possible setting would be in the production environment, would
> something like Kubernetes be responsible for setting the NUMA
> balancing attribute via prctl, or as Yafang proposed, leverage cgroup
> interface?
>
> [1] https://lore.kernel.org/lkml/fd341106e7e6cbd2f047656650f43ee87c6633c1.1787955777.git.tim.c.chen@xxxxxxxxxxxxxxx/
> [2] https://lore.kernel.org/lkml/20261012120438.52849-1-laoar.shao@xxxxxxxxx/


Thanks for taking a look and sharing the information.

A tri-state global knob sounds possible to me.

For our use case, Kubernetes or the container runtime would set the NUMA
balancing attribute via prctl(). Yafang's per-cgroup approach would also
work for us. If maintainers prefer per-cgroup control, I am happy to help
review Yafang's series.

Thanks,
Zhe

>
> thanks,
> Chenyu
>
>> [1]: https://lore.kernel.org/all/20250625102337.3128193-1-yu.c.chen@xxxxxxxxx/
>> [2]: https://lore.kernel.org/all/20230412140701.58337-1-ligang.bdlg@xxxxxxxxxxxxx/
>> [3]: https://lore.kernel.org/all/20230412141127.59741-1-ligang.bdlg@xxxxxxxxxxxxx/
>>
>> Li Zhe (4):
>>    sched/numa: Track per-process automatic NUMA balancing mode
>>    sched/numa: Add prctl controls for process mode
>>    proc: Report process NUMA balancing mode
>>    Documentation: Describe per-process NUMA balancing control
>>
>>   Documentation/admin-guide/sysctl/kernel.rst | 16 ++++++++
>>   Documentation/filesystems/proc.rst          |  6 +++
>>   fs/proc/array.c                             | 16 ++++++++
>>   include/linux/sched.h                       |  6 +++
>>   include/linux/sched/numa_balancing.h        | 42 +++++++++++++++++++++
>>   include/linux/sched/signal.h                |  8 ++++
>>   include/uapi/linux/prctl.h                  |  6 +++
>>   init/init_task.c                            |  4 ++
>>   kernel/fork.c                               |  8 ++++
>>   kernel/sched/core.c                         | 39 +++++++++++++++++++
>>   kernel/sched/fair.c                         | 36 ++++++++++++++++--
>>   kernel/sys.c                                | 18 +++++++++
>>   12 files changed, 201 insertions(+), 4 deletions(-)
>>
>> -- 
>> 2.20.1