From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id DF5ADD73EB5 for ; Sat, 31 Jan 2026 19:10:36 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 39CA46B0005; Sat, 31 Jan 2026 14:10:36 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 34A8E6B0088; Sat, 31 Jan 2026 14:10:36 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 22B826B008A; Sat, 31 Jan 2026 14:10:36 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 134796B0005 for ; Sat, 31 Jan 2026 14:10:36 -0500 (EST) Received: from smtpin13.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id A9608B95A9 for ; Sat, 31 Jan 2026 19:10:35 +0000 (UTC) X-FDA: 84393200430.13.C737192 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf24.hostedemail.com (Postfix) with ESMTP id 11E86180010 for ; Sat, 31 Jan 2026 19:10:33 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=F9t642e2; spf=pass (imf24.hostedemail.com: domain of a.hindborg@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=a.hindborg@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1769886634; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=qnUkiF8z1OkRyWv5A0exU/H6xrjIzHn/7h/Sk+Uz1r0=; b=LSJ4PW3Gvj2Qsewh6zG759KVdgIpyF/7kROYYUBM8RFNmNY6Vs20nwpp2QPayMNxDtfghk t/6BsFobA8om8CMnV1vSmLbvVnoifXribN99+gXtRNAi0fhPCrlCDgNHyy1JvTP3L0eda9 Zi6Ofb+wN/HSVlCS7jlgXC+4+SFEuYo= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=F9t642e2; spf=pass (imf24.hostedemail.com: domain of a.hindborg@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=a.hindborg@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1769886634; a=rsa-sha256; cv=none; b=Pxvcz5d5w4H2dQRgDHWP05VMqIYlOhaHaRrCsuYVNxaLULnuEf8WoBHUEr+wy90uVCr93/ GadYREp5n4834ltDrBPhNLZI40YR1xUL5t+tehWIJ+hzRLmBT2KVnXnp05VUq4C53EB0gr gmCd6ynSizaF0b9pPIN9QRQwC/FzAH4= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id C7A8F40E21; Sat, 31 Jan 2026 19:10:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A8F2CC4CEF1; Sat, 31 Jan 2026 19:10:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1769886632; bh=GGsWzZCvO7JDVG/sUiBEb6ZMfj04oe5Kx7B5vtwqH8M=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=F9t642e2FWm0TcW3noTOKtWECPb42kH34miAwJu2QzuEQFkQiGjwIV8d96l1Y40mS a/DEKfnr+blfZAuPEYYmvBaBlvcPlXs7yJUt2DQRKe/uXqEVqc5RGeVFFHNhWLzUZx XmhROLl1Tn6eCVxmo9XxpFd/EQTwfiS30oTR+rspmbZExgCwESllrrCoaCcvV4TO0B VmX4vB0oC2CGuY7O5Dcnw0GRHjYiyFeamLR2gG9y79QZf0s28p9Zr+uXGiYxCeKgnf b/v53F6Ws/fkUio1yYuCijcL7Qu/QLodMKdNkuDzqU6NFd2wTwMhiVWPORbjUyyRtJ xlamI8AAmEYhg== From: Andreas Hindborg To: Boqun Feng Cc: Gary Guo , Alice Ryhl , Lorenzo Stoakes , "Liam R. Howlett" , Miguel Ojeda , Boqun Feng , =?utf-8?Q?Bj=C3=B6rn?= Roy Baron , Benno Lossin , Trevor Gross , Danilo Krummrich , linux-mm@kvack.org, rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] rust: page: add volatile memory copy methods In-Reply-To: References: <874io3rwl3.fsf@t14s.mail-host-address-is-not-set> <871pj7ruok.fsf@t14s.mail-host-address-is-not-set> <-9VZ2SJWMomnT82Xqo2u9cSlvCYkjqUqNxfwWMTxKmah9afzYQsZfNeCs24bgYBJVw2kTN2K3YSLYGr6naR_YA==@protonmail.internalid> <87sebnqdhg.fsf@t14s.mail-host-address-is-not-set> <-5tKAwUVrj6fo337a8NWsHQBepB07jKIVI-VafwW1zp0vsGTCkBTuI5nCBniftYJePZy8kb7bhWptJ2Gc_B-kQ==@protonmail.internalid> <87pl6prkc6.fsf@t14s.mail-host-address-is-not-set> Date: Sat, 31 Jan 2026 20:10:21 +0100 Message-ID: <87jywxr42q.fsf@t14s.mail-host-address-is-not-set> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 11E86180010 X-Stat-Signature: qga8o856g1xowfcsh44cpamqdxxnki93 X-Rspam-User: X-HE-Tag: 1769886633-73984 X-HE-Meta: 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 5iQmhpVr B/7uEy2dtdWzXl/+ubICNquGH/IRIDEhhoHV/N6cnvPQLITZum4HTKr6sqcL9wgLxg0JkVCXg1cZ8plrQX49pixdRgcCHvjtY/z9EcKn9JRApjxqUUGY9Kf6jQRpD2970zqRjshHwKLKOYEbL0UlI4YaEIexVjewXi6gCHQA/8XK/TrzlMpyzGkXGmQ7P2F1Ko5Pul/HEe6XBjvwqZ+AAfsmDn42DvwOYrS+zWgHqslUR0/vZSItRLzcofeErjRrDt32b 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: "Boqun Feng" writes: > On Sat, Jan 31, 2026 at 02:19:05PM +0100, Andreas Hindborg wrote: > [..] >> > >> > However, byte-wise atomic memcpy will be more defined without paying any >> > extra penalty. >> >> Could you explain the additional penalty of `core::ptr::read_volatile` >> vs `kernel::sync::atomic::Atomic::load` with relaxed ordering? >> > > I don't understand your question, so allow me to explain what I meant: > for the sake of discussion, let's assume we have both > > fn volatile_copy_memory(src: *mut u8, dst: *mut u8, count: usize) > > and > > fn volatile_byte_wise_atomic_copy_memory(, ordering: Ordering) > > implemented. What I meant was to the best of my knowledge, when ordering > = Relaxed, these two would generate the exact same code because all the > architectures that I'm aware of have byte wise atomicity in the > load/store instructions. And compared to volatile_copy_memory(), > volatile_byte_wise_atomic_copy_memory() can bear the race with another > volatile_byte_wise_atomic_copy_memory() or any other atomic access > (meaning that's not a UB). So I'd prefer using that if we have it. Ok, thanks for clarifying. I assumed you were referring to the other functions I mentioned, because they exist in `kernel` or `core`. `volatile_copy_memory` is unstable in `core`, and as far as I know `volatile_byte_wise_atomic_copy_memory` does not exist. When you wrote `read_volatile`, I assumed you meant `core::ptr::read_volatile`, and the atomics we have are `kernel::sync::atomic::*`. So now I am a bit confused as to what method you think is usable here. Is it something we need to implement? Best regards, Andreas Hindborg