Re: [PATCH v2 05/12] powerpc: add pte_free_defer() for pgtables sharing page

[Hugh Dickins]

On Tue, 27 Jun 2023, Jason Gunthorpe wrote:
> On Wed, Jun 21, 2023 at 07:36:11PM -0700, Hugh Dickins wrote:
> > [PATCH v3 05/12] powerpc: add pte_free_defer() for pgtables sharing page
...
> Yes, this makes sense to me, very simple..
> 
> I always for get these details but atomic_dec_and_test() is a release?
> So the SetPageActive is guarenteed to be visible in another thread
> that reaches 0?

Yes, that's my understanding - so the TestClearPageActive adds more
to the guarantee than is actually needed.

"release": you speak the modern language, whereas I haven't advanced
from olden-days barriers: atomic_dec_and_test() meets atomic_t.txt's
 - RMW operations that have a return value are fully ordered;
which a quick skim of present-day memory-barriers.txt suggests would
imply both ACQUIRE and RELEASE.  Please correct me if I'm mistaken!

Hugh