Re: [PATCH net-next v3 3/3] page_pool: fix IOMMU crash when driver has already unbound

[Yunsheng Lin]

On 2024/10/26 15:33, Yunsheng Lin wrote:

...

>>>
>>> AFAIU Jakub's comment on his RFC patch for waiting, he was suggesting
>>> exactly this: Add the wait, and see if the cases where it can stall turn
>>> out to be problems in practice.
>>
>> +1
>>
>> I like Jakub's approach.
> 
> As mentioned in Toke's comment, I am still not convinced that there is some
> easy way of waiting here, doing the kick in the kernel space is hard enough,
> I am not even sure if kick need to be done or how it can be done in the user
> space if some page_pool owned page is held from user space for the cases of zero
> rx copy, io_uring and devmem tcp? killing the userspace app?
> 
> If you and Toke still think the waiting is the way out for the problem here, maybe
> we should wait for jakub's opinion and let him decide if he want to proceed with
> his waiting patch.

Is there any other suggestion/concern about how to fix the problem here?

>From the previous discussion, it seems the main concern about tracking the
inflight pages is about how many inflight pages it is needed.

If there is no other suggestion/concern , it seems the above concern might be
addressed by using pre-allocated memory to satisfy the mostly used case, and
use the dynamically allocated memory if/when necessary.