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From: Muchun Song In-Reply-To: <9c791de0-b702-1bbe-38a4-30e87d9d1b95@intel.com> Date: Thu, 18 Aug 2022 10:47:19 +0800 Cc: Miaohe Lin , Andrew Morton , Mike Kravetz , Muchun Song , Linux MM , linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: <931536E2-3948-40AB-88A7-E36F67954AAA@linux.dev> 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> <18adbf89-473e-7ba6-9a2b-522e1592bdc6@huawei.com> <9c791de0-b702-1bbe-38a4-30e87d9d1b95@intel.com> To: "Yin, Fengwei" X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660790869; 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:dkim-signature; bh=8cgTJV67VWUuGm2uD1nBwZtNeQZFKzsqmUITH2F1GjY=; b=gw2seUTLNfpZXbP5eSY/CIwMo49qtUzp0NS3RICNXUw2ohCYlsMx01Ne/Vab4r/bDJIWzi ATYr0OFq1/kNUUoJCS0q8s9l/BH0DC7cPaAT4wcoljMLYq+8PbkQ3lYFtmFWrvhVtvyapg AOtamBjwDE7FFLod9Qch1AStmdxMOjo= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=dI8UsnSe; spf=pass (imf01.hostedemail.com: domain of muchun.song@linux.dev designates 94.23.1.103 as permitted sender) smtp.mailfrom=muchun.song@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660790869; a=rsa-sha256; cv=none; b=ZXaK3AnORDAu0KS1rB1/P55HvvfvoDZplWXF+e4do67lbxFCYTkP2UDGuNrbD93przqcVv pCND/Tl97n4+kSZNb9axBiuxol3TVBTtcCE3DGYO7MUeH1ie8xkAJtnSKKm9DT32K/8UKy TL3U/HbuAvay+btDrpa+pcNza1aOwlM= Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=dI8UsnSe; spf=pass (imf01.hostedemail.com: domain of muchun.song@linux.dev designates 94.23.1.103 as permitted sender) smtp.mailfrom=muchun.song@linux.dev; dmarc=pass (policy=none) header.from=linux.dev X-Stat-Signature: mtxoq5b3qztg8pppfihoiejzapjbh638 X-Rspamd-Queue-Id: D8F234005F X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1660790868-610778 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 Aug 18, 2022, at 10:00, Yin, Fengwei wrote: >=20 >=20 >=20 > On 8/18/2022 9:55 AM, Miaohe Lin wrote: >>>>> /* >>>>> * 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=E2=80=99s >>>> contents after they have saw PG_uptodate is set. I think commit = 0ed361dec369 >>>> can tell us more details. >>>>=20 >>>> I also looked at commit 52f37629fd3c to see why we need a barrier = before >>>> set_pte_at(), but I didn=E2=80=99t find any info to explain why. I = guess we want >>>> to make sure the order between the page=E2=80=99s 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. > I have an unclear thing (not related with this patch directly): Who is = response > for the read barrier in the read side in this case? >=20 > For SetPageUptodate, there are paring write/read memory barrier. >=20 I have the same question. So I think the example proposed by Miaohe is a = little difference from the case (hugetlb_vmemmap) here. >=20 > Regards > Yin, Fengwei >=20 >=20