Re: [PATCH v3 2/7] mm: allow shared folios to be promoted to a fast tier

[David Hildenbrand (Arm)]

On 9/24/26 16:07, Gregory Price wrote:
> On Thu, Sep 24, 2026 at 01:59:15PM +0200, David Hildenbrand (Arm) wrote:
>> I wonder if a better name would just make the comment above (about memory
>> tiering) implicit and make more sense of the sysctl_numa_balancing_mode &
>> NUMA_BALANCING_MEMORY_TIERING) check.
>>
>> 	folio_promotable()
>>
>> 	folio_is_promotable()
>>
>> 	folio_numa_promotable()
>>
>> etc.
>>
>> because that seems to be what we really test with both things combined.
>>
> 
> maybe:  folio_numab_promotable() ?

Works for me if "numab" means numa balancing :)

> 
>>> -		if ((vma->vm_flags & VM_EXEC) && folio_maybe_mapped_shared(folio))
>>> +		if ((vma->vm_flags & VM_EXEC) &&
>>> +		    folio_maybe_mapped_shared(folio) &&
>>> +		    (!folio_in_lowtier(folio) || !node_is_toptier(node)))
>>>  			return -EACCES;
>>>  
>>>  		/*
>>
>> Sashiko has some comment about anonymous shared COW folios. I think it has a
>> point, but didn't look too closely.
>>
> 
> its tl;dr:
> 
> `skipping this check means those folios could end up freely migrating east-west
>  between slow tiers`
> 
> Which cannot happen (we only migrate to top tier, numab will never
> migrate *to* a slow tier).
> 
> basically false-positive

False-positive? From Sashiko? I am shocked!

-- 
Cheers,

David