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Wed, 11 May 2022 22:48:36 +0000 Received: from [10.110.48.28] (10.126.231.35) by rnnvmail201.nvidia.com (10.129.68.8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.22; Wed, 11 May 2022 15:48:36 -0700 Message-ID: Date: Wed, 11 May 2022 15:49:06 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [PATCH v4] mm: fix is_pinnable_page against on cma page Content-Language: en-US To: Minchan Kim CC: Andrew Morton , linux-mm , LKML , "Paul E . McKenney" , John Dias , David Hildenbrand References: <20220510211743.95831-1-minchan@kernel.org> <857d21da-5de2-fa3e-b1ce-41cc1cfb0191@nvidia.com> <2ffa7670-04ea-bb28-28f8-93a9b9eea7e8@nvidia.com> <54b5d177-f2f4-cef2-3a68-cd3b0b276f86@nvidia.com> From: John Hubbard In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.126.231.35] X-ClientProxiedBy: rnnvmail203.nvidia.com (10.129.68.9) To rnnvmail201.nvidia.com (10.129.68.8) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: adf4596c-c6a4-4a23-dac9-08da33a062f8 X-MS-TrafficTypeDiagnostic: BY5PR12MB4211:EE_ X-Microsoft-Antispam-PRVS: X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:12.22.5.238;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:InfoNoRecords;CAT:NONE;SFS:(13230001)(4636009)(46966006)(36840700001)(40470700004)(36860700001)(31696002)(2906002)(86362001)(36756003)(6916009)(26005)(70586007)(40460700003)(53546011)(82310400005)(2616005)(316002)(54906003)(31686004)(16576012)(47076005)(336012)(426003)(16526019)(186003)(4326008)(8676002)(70206006)(6666004)(81166007)(356005)(508600001)(5660300002)(8936002)(83380400001)(36900700001)(43740500002);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 May 2022 22:48:37.3512 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: adf4596c-c6a4-4a23-dac9-08da33a062f8 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[12.22.5.238];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CO1NAM11FT063.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR12MB4211 X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: BAED4400A3 X-Stat-Signature: 8791jgir7aujn3owhwmpuzw6dcb4ytnr X-Rspam-User: Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=Nvidia.com header.s=selector2 header.b=bV4VwQmu; spf=none (imf11.hostedemail.com: domain of jhubbard@nvidia.com has no SPF policy when checking 40.107.237.42) smtp.mailfrom=jhubbard@nvidia.com; dmarc=pass (policy=reject) header.from=nvidia.com X-HE-Tag: 1652309314-112416 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 5/11/22 15:37, Minchan Kim wrote: >> Yes. But one thing that is still unanswered, that I think you can >> answer, is: even if the compiler *did* re-read the mt variable, what >> problems could that cause? I claim "no problems", because there is >> no combination of 0, _CMA, _ISOLATE, _CMA|ISOLATE that will cause >> problems here. > > What scenario I am concerning with __READ_ONCE so compiler > inlining get_pageblock_migratetype two times are > > CPU 0 CPU 1 > alloc_contig_range > is_pinnable_page start_isolate_page_range > set_pageblock_migratetype(MIGRATE_ISOLATE) > if (get_pageeblock_migratetype(page) == MIGRATE_CMA) > so it's false > undo: > set_pageblock_migratetype(MIGRATE_CMA) > > if (get_pageeblock_migratetype(page) == MIGRATE_ISOLATE) > so it's false > > In the end, CMA memory would be pinned by CPU 0 process > so CMA allocation keep failed until the process release the > refcount. > OK, so the code checks the wrong item each time. But the code really only needs to know "is either _CMA or _ISOLATE set?". And so you can just sidestep the entire question by writing it like this: int mt = get_pageblock_migratetype(page); if (mt & (MIGRATE_ISOLATE | MIGRATE_CMA)) return false; ...yes? thanks, -- John Hubbard NVIDIA