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

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Message-ID: <2757fb07-78bf-4a39-8c60-8ca8be200994@lucifer.local>
Date: Mon, 15 Sep 2025 12:23:52 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.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 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?

So we're saying, currently, 0 means 'I will tolerate up to 511 pte_none, and eat
them all I am very very eager', and 10 means 'I will not tolerate any pte_none'
right?

Correct me if I'm wrong here! :>)

>
> --
> Cheers
>
> David / dhildenb
>

Cheers, Lorenzo