Re: [PATCH v12 mm-new 06/15] khugepaged: introduce collapse_max_ptes_none helper function

David Hildenbrand
2025-10-31T11:12:51Z

>>>> "eagerness" would not be like swappiness, and we will really have to be
>>>> careful here. I don't know yet when I will have time to look into that.
>>>
>>> I guess I missed this part of the converastion, what do you mean?
>>
>> Johannes raised issues with that on the list and afterwards we had an
>> offline discussion about some of the details and why something unpredictable
>> is not good.
>
> Could we get these details on-list so we can discuss them? This doesn't have to
> be urgent, but I would like to have a say in this or at least be part of the
> converastion please.

Sorry, I only found now time to reply on this point. Johannes raised the
point in [1], and afterwards we went a bit into detail in a off-list
discussion.

In essence, I think he is right that is something we have to be very
careful about. So it turned out as something that will take a lot more
time+effort on my side than I originally thought, turning it not
feasible in the short term given how I already lack behind on so many
other things.

So I concluded that it's probably best to have such and effort be
independent of this series. And in some way it is either way, because
max_ptes_none is just a horrible interface given the values are
architecture dependent.

I'll be happy if we can focus in this series on the bare minimum initial
support, and avoid any magic (scaling / capping) as it all turned out to
be much more tricky (interaction with the deferred shrinker ...) than
most of us initially thought.

But I think we're already on the same page here, just wanted to share a
bit more details on the max_ptes_none vs. eagerness idea.

[1] https://lkml.kernel.org/r/20250915134359.GA827803@cmpxchg.org

--
Cheers

David / dhildenb