linux-kernel - Re: [PATCH v12 mm-new 06/15] khugepaged: introduce collapse_max_ptes

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Message-ID: <a1ff622a-fd73-4707-bae8-84706a1fc2ac@lucifer.local>
Date: Tue, 28 Oct 2025 19:08:05 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: Nico Pache <npache@...hat.com>, linux-kernel@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org, linux-mm@...ck.org,
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Subject: Re: [PATCH v12 mm-new 06/15] khugepaged: introduce
 collapse_max_ptes_none helper function

On Tue, Oct 28, 2025 at 06:59:31PM +0000, Lorenzo Stoakes wrote:
> On Tue, Oct 28, 2025 at 07:08:38PM +0100, David Hildenbrand wrote:
> > >
> > > The whole concept is that we have a paramaeter whose value is _abstracted_ and
> > > which we control what it means.
> > >
> > > I'm not sure exactly why that would now be problematic? The fundamental concept
> > > seems sound no? Last I remember of the conversation this was the case.
> >
> > The basic idea was to do something abstracted as swappiness. Turns out
> > "swappiness" is really something predictable, not something we can randomly
> > change how it behaves under the hood.
> >
> > So we'd have to find something similar for "eagerness", and that's where it
> > stops being easy.
>
> I think we shouldn't be too stuck on
>

I really am the master of the unfinished sentence :)

I was going to say we shouldn't be too stuck on the analogy to swappiness and
just maintain the broad concept that eagerness is abstracted and we get to
determine what that looks like.

But absolutely I accept that it's highly sensitive and likely embodies a great
many moving parts and we must be cautious absolutely.

This is something that can be deferred for later.

Cheers, Lorenzo