Re: [v6 04/15] mm/huge_memory: implement device-private THP splitting

[David Hildenbrand <david@redhat.com>]

>>> Even if this is the only call site, there is no guarantee that
>>> there will be none in the future. I am not sure why we want caller
>>> to handle this special case. Who is going to tell the next user
>>> of RMP_USE_SHARED_ZEROPAGE or caller to try_to_map_unused_to_zeropage()
>>> that device private is incompatible with them?
>>>
>>
>> I don't disagree, but the question was why are device private pages even making
>> it to try_to_map_unused_to_zeropage()>>
> 
> Then, it could be done in remove_migration_pte():
> 
> if (rmap_walk_arg->map_unused_to_zeropage &&
> 	!folio_is_device_private(folio) &&
> 	try_to_map_unused_to_zeropage(&pvmw, folio, idx))
> 	continue;
> 
> Maybe I am too hung up on this and someone else could pat on my back and
> tell me it is OK to just do this at the only caller instead. :)

I think we shouldn't set a flag for a folio that does not make any 
sense. Just like we don't set the flag for non-anon folios?

In addition, we could add a 
VM_WARN_ON_ONCE(folio_is_device_private(folio)) in 
try_to_map_unused_to_zeropage(), to catch any future abuse.

-- 
Cheers

David / dhildenb