linux-kernel - Re: [PATCH v11 00/15] khugepaged: mTHP support

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Message-ID: <a48c8d89-da30-4a7d-96f6-e5e17757b818@redhat.com>
Date: Mon, 15 Sep 2025 13:29:22 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Kiryl Shutsemau <kas@...nel.org>, Nico Pache <npache@...hat.com>,
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Subject: Re: [PATCH v11 00/15] khugepaged: mTHP support

On 15.09.25 13:23, Lorenzo Stoakes wrote:
> On Mon, Sep 15, 2025 at 01:14:32PM +0200, David Hildenbrand wrote:
>> On 15.09.25 13:02, Lorenzo Stoakes wrote:
>>> On Mon, Sep 15, 2025 at 12:52:03PM +0200, David Hildenbrand wrote:
>>>> On 15.09.25 12:43, Lorenzo Stoakes wrote:
>>>>> On Mon, Sep 15, 2025 at 12:22:07PM +0200, David Hildenbrand wrote:
>>>>>>
>>>>>> 0 -> ~100% used (~0% none)
>>>>>> 1 -> ~50% used (~50% none)
>>>>>> 2 -> ~25% used (~75% none)
>>>>>> 3 -> ~12.5% used (~87.5% none)
>>>>>> 4 -> ~11.25% used (~88,75% none)
>>>>>> ...
>>>>>> 10 -> ~0% used (~100% none)
>>>>>
>>>>> Oh and shouldn't this be inverted?
>>>>>
>>>>> 0 eagerness = we eat up all none PTE entries? Isn't that pretty eager? :P
>>>>> 10 eagerness = we aren't eager to eat up none PTE entries at all?
>>>>>
>>>>> Or am I being dumb here?
>>>>
>>>> Good question.
>>>>
>>>> For swappiness it's: 0 -> no swap (conservative)
>>>>
>>>> So intuitively I assumed: 0 -> no pte_none (conservative)
>>>>
>>>> You're the native speaker, so you tell me :)
>>>
>>> To me this is about 'eagerness to consume empty PTE entries' so 10 is more
>>> eager, 0 is not eager at all, i.e. inversion of what you suggest :)
>>
>> Just so we are on the same page: it is about "eagerness to collapse", right?
>>
>> Wouldn't a 0 mean "I am not eager, I will not waste any memory, I am very
>> careful and bail out on any pte_none" vs. 10 meaning "I am very eager, I
>> will collapse no matter what I find in the page table, waste as much memory
>> as I want"?
> 
> Yeah, this is my understanding of your scale, or is my understanding also
> inverted? :)
> 
> Right now it's:
> 
> eagerness max_ptes_none
> 
> 0 -> 511
> ...
> 10 -> 0
> 
> Right?

Just so we are on the same page, this is what I had:

0 -> ~100% used (~0% none)

So "0" -> 0 pte_none or 512 used.

(note the used vs. none)

-- 
Cheers

David / dhildenb