Re: [PATCH v10 12/21] gpu: nova-core: mm: Add unified page table entry wrapper enums

[Joel Fernandes <joelagnelf@nvidia.com>]

> On Apr 8, 2026, at 7:13 PM, John Hubbard <jhubbard@nvidia.com> wrote:
> 
> On 4/8/26 9:58 AM, Joel Fernandes wrote:
>>> On 4/8/2026 9:26 AM, Eliot Courtney wrote:
>>> On Tue Apr 7, 2026 at 10:59 PM JST, Joel Fernandes wrote:
>>>> On 4/7/2026 9:42 AM, Eliot Courtney wrote:
>>>>> On Tue Apr 7, 2026 at 6:55 AM JST, Joel Fernandes wrote:
> ...>> [1]: https://github.com/Edgeworth/linux/commits/review/nova-mm-v10/
>> First, thanks for the effort. I looked through this, its pretty much what I
>> had before when I used traits. I don't think it is better to be honest. In
>> fact your version is worse, it adds many new types and things like the
>> following which I did not need before.
> 
> Hi Joel and all,
> 
> I also looked through Eliot's above attempt carefully, and actually
> liked it a lot (sorry! haha):
> 
> * It cleans up the code. The initial working version was readable, but
>  also had lots of noise on the screen: match statements and pairs of
>  v2/v3 statements.
> 
>  And interestingly, the mmu_version was, in effect, sporadically
>  implementing a Trait-based approach. But because it is custom,
>  readers don't benefit as much as they would with Traits, which
>  tell you immediately how things are structured.
> 
> Joel, I am passionately in agreement with your principles: code must
> be readable on the screen.
> 
> In this case, though, Traits make considerably more readable,
> especially if one makes the very reasonable assumption that readers are
> thoroughly accustomed to dealing with Rust traits.
> 
>> 
>> To put it mildly, the following suggestion should not be anywhere near my code:
>> 
> 
> lol I understand, believe me. But this is short and not too bad, really.
> 
>> /// Type-erased MMU-specific [`Vmm`] implementations.
> 
> Type erasure remains a semi-exotic thing, IMHO. As such, another
> sentence to elaborate on this would be a nice touch.
> 
>> enum VmmInner {
>>    /// `Vmm` implementation for MMU v2.
>>    V2(VmmImpl<MmuV2>),
>>    /// `Vmm` implementation for MMU v3.
>>    V3(VmmImpl<MmuV3>),
>> }
>> 
>> /// MMU-specific [`Vmm`] implementation.
>> struct VmmImpl<M: Mmu> {
>> 
>> Seriously, I have to pass on this. :-)
>> 
>> And, you unfortunately seem to have ignored my point about requiring 4 NEW
>> traits (Mmu, PteOps, PdeOps, DualPdeOps etc), which I did not need before.
>> So you're making the code much much worse than before actually. We don't
>> new traits and types pointlessly.
> 
> They are not pointless.
> 
> However! What I think would be nice is: do a new v11 with approximately
> this approach, and then we can beat it into being as readable as
> possible.

Since it is 3 against 1 here, I rest my case :-). I am still in
disagreement since I do not see much benefit (that is why I said
pointless above). Actually it is not even about readability, that is
subjective (and I haven’t heard most people say parametrizing code for
the sake of it makes it more readable anyway). It is that the code gen
is worse, and the complexity is just moved to a higher level in the
code, not removed. So what are we getting out of this really, other than
more boiler plate in higher layers of the code that did not exist
before? Not performance, not better generated code. Really nothing. See
all the data points in my previous reply.

Note that if the mmu version threading bothers everyone so much, we can
also pass down chipset instead and let the walker deal with determining
versioning. Would that be better?

But otherwise and since you guys asked, here comes a parameterized v11... ;-).
  (Coming next week since this week I’m working on IRQ handling).

thanks,

-- 
Joel Fernandes