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

[David Hildenbrand (Arm)]

On 10/28/26 10:58, John Paul Adrian Glaubitz wrote:
> 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,
>>>
>>>
>>> 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.

sparc64 machines?! cmon

> 
>> 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.

No. Run stable kernels.

> 
>> 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.

Follow the discussion.

> 
>> 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.

"Very recent" find the mistake.

(sorry, I'm unusually grumpy today)

-- 
Cheers,

David