linux-kernel - Re: [PATCH v2 05/12] powerpc: add pte_free

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Message-ID: <7b1be7d-9287-cbc6-ef7-55e44625e4e@google.com>
Date:   Tue, 27 Jun 2023 13:53:17 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
cc:     Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
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Subject: Re: [PATCH v2 05/12] powerpc: add pte_free_defer() for pgtables
 sharing page

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