Re: [PATCH v3 3/7] sched/numa: scan read-only file mappings in tiering mode

[Gregory Price]

On Thu, Sep 24, 2026 at 10:53:56PM +0200, David Hildenbrand (Arm) wrote:
> > +		placement_scan &= numab_mode & NUMA_BALANCING_NORMAL;
> 
> Do we have to update placement_scan at all?

in the following commits this composes:

	placement_scan &= numab_mode & NUMA_BALANCING_NORMAL;
	if (scan_started)
		placement_scan &= vma->numab_state->placement_scan;
	else if (tiering)
		placement_scan &= placement_due;

But i'll think about this when I update the function name.

> 
> Can't we do:
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 8a4687f67d82f..fc8862ee31442 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4121,6 +4121,7 @@ static void task_numa_work(struct callback_head *work)
>  {
>         const unsigned int numab_mode = READ_ONCE(sysctl_numa_balancing_mode);
>         const bool tiering = numab_mode & NUMA_BALANCING_MEMORY_TIERING;
> +       const bool balancing = numab_mode & NUMA_BALANCING_NORMAL;
>         unsigned long migrate, next_scan, now = jiffies;
>         struct task_struct *p = current;
>         struct mm_struct *mm = p->mm;
> @@ -4313,9 +4314,8 @@ static void task_numa_work(struct callback_head *work)
>                         continue;
>                 }
> 
> -               placement_scan &= numab_mode & NUMA_BALANCING_NORMAL;
>                 cp_flags = MM_CP_PROT_NUMA;
> -               if (!placement_scan)
> +               if (!placement_scan || !balancing)
>                         cp_flags |= MM_CP_PROT_NUMA_PROMO_ONLY;
> 
>                 do {
> 
> (maybe I messed up my boolean algreba, it's late)
> 
> -- 
> Cheers,
> 
> David
>