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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 3B2F9C433DB for ; Thu, 21 Jan 2021 21:40:57 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CB4BD23A56 for ; Thu, 21 Jan 2021 21:40:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CB4BD23A56 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 1D84C6B0006; Thu, 21 Jan 2021 16:40:56 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 187086B0007; Thu, 21 Jan 2021 16:40:56 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 09DF16B0008; Thu, 21 Jan 2021 16:40:56 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0110.hostedemail.com [216.40.44.110]) by kanga.kvack.org (Postfix) with ESMTP id E76036B0006 for ; Thu, 21 Jan 2021 16:40:55 -0500 (EST) Received: from smtpin05.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 8DAF43637 for ; Thu, 21 Jan 2021 21:40:55 +0000 (UTC) X-FDA: 77731102470.05.lace54_4b1399027566 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin05.hostedemail.com (Postfix) with ESMTP id 25A8718032807 for ; Thu, 21 Jan 2021 21:40:55 +0000 (UTC) X-HE-Tag: lace54_4b1399027566 X-Filterd-Recvd-Size: 3347 Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by imf10.hostedemail.com (Postfix) with ESMTP for ; Thu, 21 Jan 2021 21:40:52 +0000 (UTC) IronPort-SDR: I/jFVLa8m0iYBajZfSt9JsWpvLPnfc0HZoM2iHjU33Cqd0kP6+/Zdgl6iBv/K9N4pwjC68EhiQ g158tcaXAXwA== X-IronPort-AV: E=McAfee;i="6000,8403,9871"; a="179436057" X-IronPort-AV: E=Sophos;i="5.79,365,1602572400"; d="scan'208";a="179436057" Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Jan 2021 13:40:50 -0800 IronPort-SDR: u+JpUjjQSXfUXGLMAXw5NU/pwznQ/bNs8S+w5N5NH/wdP5atFQQCvDp7F07Fk3vKwlzciE8b70 SLxX92CVOZxg== X-IronPort-AV: E=Sophos;i="5.79,365,1602572400"; d="scan'208";a="571851418" Received: from yyu32-mobl1.amr.corp.intel.com (HELO [10.209.46.254]) ([10.209.46.254]) by fmsmga006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Jan 2021 13:40:47 -0800 Subject: Re: [PATCH v17 08/26] x86/mm: Introduce _PAGE_COW To: Borislav Petkov 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 References: <20201229213053.16395-1-yu-cheng.yu@intel.com> <20201229213053.16395-9-yu-cheng.yu@intel.com> <20210121184405.GE32060@zn.tnic> <20210121204113.GG32060@zn.tnic> From: "Yu, Yu-cheng" Message-ID: <56a7b904-dddc-d92c-b74f-552f9738b8ac@intel.com> Date: Thu, 21 Jan 2021 13:40:46 -0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <20210121204113.GG32060@zn.tnic> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit 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 1/21/2021 12:41 PM, Borislav Petkov wrote: > 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. > Ok, I will change it to the more readable code as stated earlier. -- Yu-cheng