Re: [PATCH v3 4/4] mm: pass the number of PTEs to move_pte()

[John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>]

Hi David,

On Wed, 2026-10-28 at 10:22 +0100, David Hildenbrand (Arm) wrote:
> On 10/28/26 10:16, Imre Kaloz wrote:
> > Hi David,
> > 
> > On 10/28/26 09:49, David Hildenbrand (Arm) wrote:
> > > But that's too complicated, requiring page table walks ....
> > > People running museum piece hardware and complaining about performance of mremap
> > > or memory reclaim should reconsider life choices.
> > 
> > I'm one of the museum folks myself, though more the kind who loves
> > running a modern kernel on old hardware than the kind who complains
> > about it :) A lot of these machines are still doing real work, and
> > these days not everyone can, or wants to, just buy a new computer.
> > 
> > Some of us spend our time keeping these platforms working, and I'm
> > not asking anyone else to carry that, which is why I tried to keep
> > all of it in sparc.
> 
> Okay, so mremap() and reclaim memory performance concerns make you sleep bad at
> night? :)
> 
> Don't get me wrong, I know that running new kernels on old HW is fun.
> 
> Last week a got upstream Linux running on a 32bit x86 notebook from 2007 with
> the snap of a finger. Everything just works (using Alpine).

That's cool!

> I couldn't care less about performance. Nobody should.

Well, try to put it into some perspective: For some people, old hardware
is all what they have and given the current high prices, I assume many
people will be stuck with old hardware for a while now. Think of developing
countries as well.

> The biggest problem all of us with supporting old hardware is the maintanance
> cost. Not just core-mm, but also things like ad-hoc page table walkers you are
> adding we (from core-mm) might have to touch at some point.

Well, but if people are using it in the end, I think it's justified to support it.

> If there is no good reason for the complexity, out it goes.

The patch doesn't really look that complex though. It adds an additional parameter
to move_pte() which adds a few more lines of code. Not really overly complex, I think.

> Because otherwise people will push more and more for removing legacy support
> completely, and that's not what you want, right?

I don't think it's fair to make the kernel exclusive to very recent hardware only.

Adrian
> 

-- 
 .''`.  John Paul Adrian Glaubitz
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`. `'   Physicist
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