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

Michal Hocko
2022-10-12T12:15:16Z

On Wed 12-10-22 19:22:21, Zhongkun He wrote:
> >
> > 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?

We already do that via mpol_{get,put} but there are cases where the
reference counting is ignored because it cannot be freed and also mpol_cond_put
resp. open coded versions of mpol_needs_cond_ref.
--
Michal Hocko
SUSE Labs