Re: [PATCH v3 4/7] sched/numa: separate VMA placement from scan continuation

[David Hildenbrand (Arm)]

>  		/*
> -		 * Do not scan the VMA if task has not accessed it, unless no other
> -		 * VMA candidate exists.
> +		 * Do not scan the VMA if a task has not accessed it, unless no other
> +		 * VMA candidate exists. If a scan is already in-progress, finish it,
> +		 * but track continuation separately from starting a new one.
>  		 */
> -		if (!vma_pids_forced && !vma_is_accessed(mm, vma)) {
> -			vma_pids_skipped = true;
> -			trace_sched_skip_vma_numa(mm, vma, NUMAB_SKIP_PID_INACTIVE);
> -			continue;
> +		placement_due = vma_needs_placement_scan(mm, vma);
> +		scan_started = mm->numa_scan_offset > vma->vm_start;
> +		pid_scan_allowed = vma_pids_forced || placement_due;
> +
> +		if (!pid_scan_allowed) {
> +			if (scan_started) {
> +				trace_sched_skip_vma_numa(mm, vma, NUMAB_SKIP_IGNORE_PID);
> +			} else {
> +				vma_pids_skipped = true;
> +				trace_sched_skip_vma_numa(mm, vma, NUMAB_SKIP_PID_INACTIVE);
> +				continue;
> +			}
>  		}
>  
> +		/* Keep scan policy stable while processing a VMA in chunks.*/
>  		placement_scan &= numab_mode & NUMA_BALANCING_NORMAL;
> +		if (scan_started)
> +			placement_scan &= vma->numab_state->placement_scan;

Besides avoiding the "&=" in all cases to make the code readable, nothing caught
my attention.

It's all very complicated, so I won't pretend I fully digested the logic :)

-- 
Cheers,

David