Re: [PATCH v2 3/4] sched/numa: scan read-only file mappings in tiering mode

[Gregory Price]

On Fri, Sep 18, 2026 at 02:58:36PM +0200, David Hildenbrand (Arm) wrote:
> > +/*
> > + * Read-only file-backed mappings are expected to be cache replicated between
> > + * accessor nodes, so they are not worth sampling for placement.  They can
> > + * still strand on the slow tier like anything else.
> > + */
> > +static bool vma_is_ro_file(struct vm_area_struct *vma)
> > +{
> > +	return vma->vm_file && (vma->vm_flags & (VM_READ | VM_WRITE)) == VM_READ;
> 
> 
> MAP_PRIVATE can easily map a read-only file with write permissions. So the
> function name is a bit misleading.
> 
> This smells like a helper that should go next to other vma helpers and have
> clear semantics.
> 

No argument here.  Would like to balance improvement vs backportable
bugfix though.  I broke out the name to try to make it at least a bit
more readable.

> >  		if (!vma->vm_mm ||
> > -		    (vma->vm_file && (vma->vm_flags & (VM_READ|VM_WRITE)) == (VM_READ))) {
> > +		    (vma_is_ro_file(vma) &&
> > +		     !(numab_mode & NUMA_BALANCING_MEMORY_TIERING))) {
> 
> I'd vote for >80c here and but it into a singe line.
> 
> Or just use a magical helper
> 
> const bool tiering = numab_mode & NUMA_BALANCING_MEMORY_TIERING;
> 
> or sth like that.
> 

ack

> >  			trace_sched_skip_vma_numa(mm, vma, NUMAB_SKIP_SHARED_RO);
> >  			continue;
> >  		}
> > @@ -4306,7 +4316,8 @@ static void task_numa_work(struct callback_head *work)
> >  			continue;
> >  		}
> >  
> > -		promo_only = !(numab_mode & NUMA_BALANCING_NORMAL);
> > +		promo_only = !(numab_mode & NUMA_BALANCING_NORMAL) ||
> > +			     vma_is_ro_file(vma);
> 
> As I said, maybe that flag could be voided.
> 

ack.