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[209.85.208.44]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a80f414bbf3sm94258366b.145.2024.08.13.12.48.26 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 13 Aug 2024 12:48:26 -0700 (PDT) Received: by mail-ed1-f44.google.com with SMTP id 4fb4d7f45d1cf-5ba43b433beso6351465a12.1 for ; Tue, 13 Aug 2024 12:48:26 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCXj+yfuzHpgrSvq/lECcUe2bbFFATmFxoj7jCcZBDo0kiclzKp8GAXAJSARMWGXZ8Vqr3KDf/SJTX3d8vGQW9l3kHs= X-Received: by 2002:a05:6402:2102:b0:5af:758a:6934 with SMTP id 4fb4d7f45d1cf-5bea1bf27c2mr540434a12.0.1723578506092; Tue, 13 Aug 2024 12:48:26 -0700 (PDT) MIME-Version: 1.0 References: <20240813-seq_optimize-v1-1-84d57182e6a7@gentwo.org> <183ee6fa-1d42-4a01-8446-4f20942680d2@redhat.com> In-Reply-To: <183ee6fa-1d42-4a01-8446-4f20942680d2@redhat.com> From: Linus Torvalds Date: Tue, 13 Aug 2024 12:48:09 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH RFC] Avoid memory barrier in read_seqcount() through load acquire To: Waiman Long Cc: cl@gentwo.org, Catalin Marinas , Will Deacon , Peter Zijlstra , Ingo Molnar , Boqun Feng , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: aj3t5a3p9crooneuoxr14okm7k6hyhn4 X-Rspam-User: X-Rspamd-Queue-Id: 872B9100008 X-Rspamd-Server: rspam02 X-HE-Tag: 1723578509-801564 X-HE-Meta: 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 BINVqISM QkH8CouAptFv7d04/TBcXrgg5dBBQYdRBVw378aV7yg+DTAZkmQRc0dXY2SlVbs6Lcvwi1acz/CzkRVt/wswG4uN4aTuvdIdFhNtzQyRB9KGe+pnTj0wcfix+pWEbIqpu6bJ8eWiLJobb81g6s2PqC5wZj8dmTHnihBISNJw64rvIOlXgBnEAmov50bA0VpHk90guiuM2rBD3RxkunHeWrf9z1l86p/H44AblEWLJ0aP4S0zTY9BDIQZH3DspvOaM47q/p4eGFodD3wEKW0nEDL0oPOL5RIeqOz3JRt/WrZdQIE7cMKD20PT9Gj19u+4DCA7I7tm/YukD317UACky76T2XJfkfKO6Rvk+9dWw5kUIyPePgHJQUQndKQe3syK5pnDnfW1fPYlu0sC/Quu7zfCAkNsCraKZJnHkq4UFKlNmABGYKtZP2vy7fDBMV4oVj2Dr3s7oN1qs3RTB9GVtbiNp942fDnb0CT+RS8jUmUF1jEFOzIAYrrBhZTk5RHnyboUEbGSSWVPX3u5HyCUc7D7R/dxNv69jP8zNnMG7dQeqtTaivIjWLGHfUzvEmBmzVnx2gkou7xoEN7e4uPu4AUc2ICE70x0KSEhsJb1GsYIcTm+zhkS9xgi3idbhAXP3hr31Fb/GL0zQ3cQ= 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: List-Subscribe: List-Unsubscribe: On Tue, 13 Aug 2024 at 12:01, Waiman Long wrote: > > Do we need a new ARCH flag? I'm confused by that question. That's clearly exactly what that ARCH_HAS_ACQUIRE_RELEASE is. Obviously all architectures "have" it - in the sense that we always have access to a "smp_load_acquire()/smp_store_release()". But if the architecture doesn't support it natively, the old rmb/wmb model may be preferred. Although maybe we're at the point where we don't even care about that. Linus