Re: [PATCH v2 3/5] mm: add static PMD zero page

[David Hildenbrand <david@redhat.com>]

On 17.07.25 12:34, Pankaj Raghav (Samsung) wrote:
>>> Then, we'd only need a config option to allow for that to happen.
>>
>> Something incomplete and very hacky just to give an idea. It would try allocating
>> it if there is actual code running that would need it, and then have it
>> stick around forever.
>>
> Thanks a lot for this David :) I think this is a much better idea and
> reduces the amount code and reuse the existing infrastructure.
> 
> I will try this approach in the next version.
> 
> <snip>
>> +       /*
>> +        * Our raised reference will prevent the shrinker from ever having
>> +        * success -> static.
>> +        */
>> +       if (atomic_read(&huge_zero_folio_is_static))
>> +               return huge_zero_folio;
>> +       /* TODO: memblock allocation if buddy is not up yet? Or Reject that earlier. */
> 
> Do we need memblock allocation? At least the use cases I forsee for
> static pmd zero page are all after the mm is up. So I don't see why we
> need to allocate it via memblock.

Even better!

We might want to detect whether allocation of the huge zeropage failed a 
couple of times and then just give up. Otherwise, each and every user of 
the largest zero folio will keep allocating it.

-- 
Cheers,

David / dhildenb