Re: [PATCH v3 13/13] mm: introduce arch_wants_lazy_mmu_mode()

Kevin Brodsky
2025-10-24T12:17:31Z

On 23/10/2025 22:10, David Hildenbrand wrote:
> On 15.10.25 10:27, Kevin Brodsky wrote:
>> powerpc decides at runtime whether the lazy MMU mode should be used.
>>
>> To avoid the overhead associated with managing
>> task_struct::lazy_mmu_state if the mode isn't used, introduce
>> arch_wants_lazy_mmu_mode() and bail out of lazy_mmu_mode_* if it
>> returns false. Add a default definition returning true, and an
>> appropriate implementation for powerpc.
>>
>> Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
>> ---
>> This patch seemed like a good idea to start with, but now I'm not so
>> sure that the churn added to the generic layer is worth it.
>
> Exactly my thoughts :)
>
> I think we need evidence that this is really worth it for optimizing
> out basically a counter update on powerpc.

Ack, I'll drop that patch in v4 unless someone sees a better
justification for it.

- Kevin