Re: [External] Re: [RFC] mm: add new syscall pidfd_set_mempolicy()

Zhongkun He
2022-10-12T11:22:31Z

>
> Yes, this will require some refactoring and one potential way is to make
> mpol ref counting unconditional. The conditional ref. counting has
> already caused issues in the past and the code is rather hard to follow
> anyway. I am not really sure this optimization is worth it.
>
> Another option would be to block the pidfd side of things on completion
> which would wake it up from the task_work context but I would rather
> explore the ref counting approach first and only if this is proven to be
> too expensive to go with hacks like this.

Hi Michal

The counting approach means executing mpol_get/put() when start/finish
using mempolicy,right? With the addition of lock add/dec on the hot
path, the performance may be degraded.

I'll try it to see its performance impact in detail.

Thanks.