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 X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 36AFDC433DB for ; Thu, 21 Jan 2021 20:41:24 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id BE26B2389F for ; Thu, 21 Jan 2021 20:41:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BE26B2389F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=alien8.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 255046B0006; Thu, 21 Jan 2021 15:41:23 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 206BE6B0007; Thu, 21 Jan 2021 15:41:23 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0F4B16B0008; Thu, 21 Jan 2021 15:41:23 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0081.hostedemail.com [216.40.44.81]) by kanga.kvack.org (Postfix) with ESMTP id ED3256B0006 for ; Thu, 21 Jan 2021 15:41:22 -0500 (EST) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id B214E180AD80F for ; Thu, 21 Jan 2021 20:41:22 +0000 (UTC) X-FDA: 77730952404.17.lock64_0111adc27566 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin17.hostedemail.com (Postfix) with ESMTP id 94D19180D0181 for ; Thu, 21 Jan 2021 20:41:22 +0000 (UTC) X-HE-Tag: lock64_0111adc27566 X-Filterd-Recvd-Size: 3227 Received: from mail.skyhub.de (mail.skyhub.de [5.9.137.197]) by imf47.hostedemail.com (Postfix) with ESMTP for ; Thu, 21 Jan 2021 20:41:20 +0000 (UTC) Received: from zn.tnic (p200300ec2f157500fb5fde66f083fa9c.dip0.t-ipconnect.de [IPv6:2003:ec:2f15:7500:fb5f:de66:f083:fa9c]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 5DBEB1EC026D; Thu, 21 Jan 2021 21:41:18 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1611261678; h=from:from: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; bh=6wzwOhvBmSjSU2bMPkrqdBsoyczaTsVK0FjOw4Itbks=; b=P40vr2r0ywK6EjiClnHStP/a+gYoB8gULMgUma93Tz4K4DF/kykiyHsK0ccTCuBZ/Usj9v USFijhl/n+2TvBmcdHu+wQYPZyKbbMo3tkuBsQHdihbtmYgjeoSFlNKHcGh4K0TBxmhz2A y/TI7VTHBegmKLZD0IpL81KaKeuwB+Y= Date: Thu, 21 Jan 2021 21:41:13 +0100 From: Borislav Petkov To: "Yu, Yu-cheng" Cc: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin , Weijiang Yang , Pengfei Xu Subject: Re: [PATCH v17 08/26] x86/mm: Introduce _PAGE_COW Message-ID: <20210121204113.GG32060@zn.tnic> References: <20201229213053.16395-1-yu-cheng.yu@intel.com> <20201229213053.16395-9-yu-cheng.yu@intel.com> <20210121184405.GE32060@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: 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, Jan 21, 2021 at 12:16:23PM -0800, Yu, Yu-cheng wrote: > It clears _PAGE_DIRTY and sets _PAGE_COW. That is, > > if (pte.pte & _PAGE_DIRTY) { > pte.pte &= ~_PAGE_DIRTY; > pte.pte |= _PAGE_COW; > } > > So, shifting makes resulting code more efficient. Efficient for what? Is this a hot path? If not, I'd take readable code any day of the week. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette