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]) by smtp.lore.kernel.org (Postfix) with ESMTP id BA746C32771 for ; Thu, 18 Aug 2022 01:55:39 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DFB378D0002; Wed, 17 Aug 2022 21:55:38 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DABA46B0074; Wed, 17 Aug 2022 21:55:38 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C71818D0002; Wed, 17 Aug 2022 21:55:38 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id B781D6B0073 for ; Wed, 17 Aug 2022 21:55:38 -0400 (EDT) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 8100F120AA9 for ; Thu, 18 Aug 2022 01:55:38 +0000 (UTC) X-FDA: 79811046756.16.75C3213 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by imf08.hostedemail.com (Postfix) with ESMTP id A46301601D8 for ; Thu, 18 Aug 2022 01:55:37 +0000 (UTC) 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 ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=none; spf=pass (imf08.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660787738; a=rsa-sha256; cv=none; b=WXU/vfwHW4ss5jS/D/4xzG7761H1MEDHbNwWUO8VHjwRE6m3ysVfJu89fefroJLi1rHuB8 kiBYrtYrg0FBSP2U5hL1EcEREYiHIy57QsbDSurlbGDMnglZvOoT4yrhJ+nR4kdzSIYcJv Cd/N2tXgsCCswgBAy6LAVsKVIVKi7h8= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660787738; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=U3AT8N9U9NiZiDPOK0mhbhcipWTQAB/jklnUEyIGK8g=; b=UpyDLvu1/+5RFo8wejiFGg1DdF0cVUl7nJdeQXqIBQbPsTDfTIptUb0c8erY/z0vAeUftv gATwyQsCN/xSTh/R0HZG+RAoWL8R5xUtW6z9MCdZgAhhRrHrov2t5qMtWGJ55uAwy5Y2gD aS8Mk020vKFwiLpdz3Mi/Hki9YhHf9k= Authentication-Results: imf08.hostedemail.com; dkim=none; spf=pass (imf08.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-Stat-Signature: pp3bo9gemq9hqsfgejx1c8tq48m859tn X-Rspamd-Queue-Id: A46301601D8 X-Rspamd-Server: rspam06 X-Rspam-User: X-HE-Tag: 1660787737-452591 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 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