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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qUDWL-00Et27-RY; Thu, 10 Aug 2023 21:48:41 +0000 Date: Thu, 10 Aug 2023 22:48:41 +0100 From: Matthew Wilcox To: Peter Xu Cc: David Hildenbrand , Ryan Roberts , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, Andrew Morton , Jonathan Corbet , Mike Kravetz , Hugh Dickins , Yin Fengwei , Yang Shi , Zi Yan Subject: Re: [PATCH mm-unstable v1] mm: add a total mapcount for large folios Message-ID: References: <20230809083256.699513-1-david@redhat.com> <155bd03e-b75c-4d2d-a89d-a12271ada71b@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 8B18D4000D X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 1agd3ss4w5br1yojjm5p18tqsqtdsjs1 X-HE-Tag: 1691704133-998404 X-HE-Meta: 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 bsSfa7/3 zdFyeWVs8ov1masHyquu/3sFW3H+z5Csp0UqfFEj5MC/PdXHKbtAWel5P3cIWeeGRs6Nl+0DU0u8N/bDOes3Al9tqg0UtKfHEj9M7W7vIwu0UngqwVhQ6EBChAddoomfr096TawO7a3UbhB9jRTRVM6+m6qwAau3XoQPr X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Aug 10, 2023 at 04:57:11PM -0400, Peter Xu wrote: > AFAICS if that patch was all correct (while I'm not yet sure..), you can > actually fit your new total mapcount field into page 1 so even avoid the > extra cacheline access. You can have a look: the trick is refcount for > tail page 1 is still seems to be free on 32 bits (if that was your worry > before). Then it'll be very nice if to keep Hugh's counter all in tail 1. No, refcount must be 0 on all tail pages. We rely on this in many places in the MM.