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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AD20FC25B08 for ; Thu, 18 Aug 2022 01:55:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242637AbiHRBzh (ORCPT ); Wed, 17 Aug 2022 21:55:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35842 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242167AbiHRBzg (ORCPT ); Wed, 17 Aug 2022 21:55:36 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6A032520A1 for ; Wed, 17 Aug 2022 18:55:35 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.54]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4M7SZ45yPbzlVj4; Thu, 18 Aug 2022 09:52:28 +0800 (CST) Received: from [10.174.177.76] (10.174.177.76) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 18 Aug 2022 09:55:33 +0800 Subject: Re: [PATCH 4/6] mm: hugetlb_vmemmap: add missing smp_wmb() before set_pte_at() To: "Yin, Fengwei" , Muchun Song CC: Andrew Morton , Mike Kravetz , Muchun Song , Linux MM , References: <20220816130553.31406-1-linmiaohe@huawei.com> <20220816130553.31406-5-linmiaohe@huawei.com> <0EAF1279-6A1C-41FA-9A32-414C36B3792A@linux.dev> <019c1272-9d01-9d51-91a0-2d656b25c318@intel.com> From: Miaohe Lin Message-ID: <18adbf89-473e-7ba6-9a2b-522e1592bdc6@huawei.com> Date: Thu, 18 Aug 2022 09:55:32 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <019c1272-9d01-9d51-91a0-2d656b25c318@intel.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/8/18 9:14, Yin, Fengwei wrote: > > > On 8/17/2022 7:21 PM, Muchun Song wrote: >> >> >>> On Aug 17, 2022, at 16:41, Miaohe Lin wrote: >>> >>> On 2022/8/17 10:53, Muchun Song wrote: >>>> >>>> >>>>> On Aug 16, 2022, at 21:05, Miaohe Lin wrote: >>>>> >>>>> The memory barrier smp_wmb() is needed to make sure that preceding stores >>>>> to the page contents become visible before the below set_pte_at() write. >>>> >>>> I’m not sure if you are right. I think it is set_pte_at()’s responsibility. >>> >>> Maybe not. There're many call sites do the similar things: >>> >>> hugetlb_mcopy_atomic_pte >>> __do_huge_pmd_anonymous_page >>> collapse_huge_page >>> do_anonymous_page >>> migrate_vma_insert_page >>> mcopy_atomic_pte >>> >>> Take do_anonymous_page as an example: >>> >>> /* >>> * The memory barrier inside __SetPageUptodate makes sure that >>> * preceding stores to the page contents become visible before >>> * the set_pte_at() write. >>> */ >>> __SetPageUptodate(page); >> >> IIUC, the case here we should make sure others (CPUs) can see new page’s >> contents after they have saw PG_uptodate is set. I think commit 0ed361dec369 >> can tell us more details. >> >> I also looked at commit 52f37629fd3c to see why we need a barrier before >> set_pte_at(), but I didn’t find any info to explain why. I guess we want >> to make sure the order between the page’s contents and subsequent memory >> accesses using the corresponding virtual address, do you agree with this? > This is my understanding also. Thanks. That's also my understanding. Thanks both. Thanks, Miaohe Lin