Re: [PATCH 6/6] sched/numa: ignore preferred nodes without normal balancing

[Gregory Price <gourry@gourry.net>]

On Wed, Oct 14, 2026 at 05:43:47PM +0800, Li Zhe wrote:
> numa_preferred_nid is normal AutoNUMA task-placement state.
> Memory-tiering-only mode uses NUMA hint faults to drive page promotion,
> not CPU placement.
> 
> Even after tiering-only faults stop updating normal placement statistics,
> a task can still have a preferred NUMA node from earlier normal balancing
> or from previously polluted state. Several scheduler paths consume that
> stale state when the NUMA balancing static key is enabled, including
> explicit NUMA task migration, sched-cache preferred LLC and scan CPU mask
> selection, load-balance locality checks, fbq classification, and wakeup
> group selection.
> 
> Add a small helper for normal NUMA placement being enabled and use it to
> ignore numa_preferred_nid when NUMA_BALANCING_NORMAL is disabled. Keep
> the preferred-node migration retry timestamp update before the normal-mode
> check so accepted non-normal sysctl states do not leave stale retry state
> behind.
> 
> Keep the rq nr_numa_running and nr_preferred_running accounting unchanged
> so runtime mode changes do not make enqueue/dequeue accounting asymmetric;
> the load balancer simply stops consuming those counters while normal
> balancing is off.
> 
> This does not clear numa_preferred_nid and does not change memory-tiering
> promotion decisions.
> 

Same feedback - need to present user-facing performance changes to show
the impact of this change.

Sashiko also has some correctness feedback.

~Gregory