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

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Message-ID: <85aa2020-5b5e-4bfc-aade-581d20aeff87@lucifer.local>
Date: Mon, 15 Sep 2025 11:32:18 +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 12:25:54PM +0200, David Hildenbrand wrote:
> > >
> > > I would just say "The kernel might decide to use a more conservative approach
> > > when collapsing smaller THPs" etc.
> > >
> > >
> > > Thoughts?
> >
> > Well I've sort of reviewed oppositely there :) well at least that it needs to be
> > a hell of a lot clearer (I find that comment really compressed and I just don't
> > really understand it).
>
> Right. I think these are just details we should hide from the user. And in
> particular, not over-document it so we can more easily change semantics
> later.

And when we change semantics we can't change comments?

I mean maybe we're talking across purposes here, I'm talking about code
comments, not the documentation.

I agree the documentation should not mention any of this.

>
> >
> > I guess I didn't think about people reading that and relying on it, so maybe we
> > could alternatively make that succinct.
> >
> > But I think it'd be better to say something like "mTHP collapse cannot currently
> > correctly function with half or more of the PTE entries empty, so we cap at just
> > below this level" in this case.
>
> IMHO we should just say that the value might be reduced for internal
> purposes and that this behavior might change in the future would likely be
> good enough.

Again, I assume you mean documentation rather than comments?

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

Cheers, Lorenzo