Message-ID: <6ec80746-2945-485f-930e-8cc34446f9e3@redhat.com>
Date: Mon, 15 Sep 2025 13:45:39 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
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Subject: Re: [PATCH v11 00/15] khugepaged: mTHP support

On 15.09.25 13:35, Lorenzo Stoakes wrote:
> On Mon, Sep 15, 2025 at 01:29:22PM +0200, David Hildenbrand wrote:
>> 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)
> 
> OK right so we're talking about the same thing, I guess?
> 
> I was confused partly becuase of the scale, becuase weren't people setting
> this parameter to low values in practice?
> 
> And now we make it so we have equivalent of:
> 
> 0 -> 0
> 1 -> 256
> 2 -> 384

Ah, there is the problem, that's not what I had in mind.

0 -> ~100% used (~0% none)
...
8 -> ~87,5% used (~12.5% none)
9 -> ~75% used (~25% none)
9 -> ~50% used (~50% none)
10 -> ~0% used (~100% none)

Hopefully I didn't mess it up again.

-- 
Cheers

David / dhildenb

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