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Thu, 25 Feb 2021 00:33:54 +0000 Subject: Re: [PATCH v7 2/6] userfaultfd: disable huge PMD sharing for MINOR registered VMAs To: Axel Rasmussen , Alexander Viro , Alexey Dobriyan , Andrea Arcangeli , Andrew Morton , Anshuman Khandual , Catalin Marinas , Chinwen Chang , Huang Ying , Ingo Molnar , Jann Horn , Jerome Glisse , Lokesh Gidra , "Matthew Wilcox (Oracle)" , Michael Ellerman , =?UTF-8?Q?Michal_Koutn=c3=bd?= , Michel Lespinasse , Mike Rapoport , Nicholas Piggin , Peter Xu , Shaohua Li , Shawn Anastasio , Steven Rostedt , Steven Price , Vlastimil Babka Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Adam Ruprecht , Cannon Matthews , "Dr . David Alan Gilbert" , David Rientjes , Mina Almasry , Oliver Upton References: <20210219004824.2899045-1-axelrasmussen@google.com> <20210219004824.2899045-3-axelrasmussen@google.com> From: Mike Kravetz Message-ID: Date: Wed, 24 Feb 2021 16:33:51 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 In-Reply-To: <20210219004824.2899045-3-axelrasmussen@google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [50.38.35.18] X-ClientProxiedBy: MWHPR12CA0040.namprd12.prod.outlook.com (2603:10b6:301:2::26) To BY5PR10MB4196.namprd10.prod.outlook.com (2603:10b6:a03:20d::23) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.2.112] (50.38.35.18) by MWHPR12CA0040.namprd12.prod.outlook.com (2603:10b6:301:2::26) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3890.19 via Frontend Transport; Thu, 25 Feb 2021 00:33:53 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 297862a9-46a9-49fb-1f1a-08d8d92507ff X-MS-TrafficTypeDiagnostic: BYAPR10MB2951: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:8273; 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identity=mailfrom; envelope-from=""; helo=aserp2120.oracle.com; client-ip=141.146.126.78 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1614213275-218029 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 2/18/21 4:48 PM, Axel Rasmussen wrote: > As the comment says: for the MINOR fault use case, although the page > might be present and populated in the other (non-UFFD-registered) half > of the mapping, it may be out of date, and we explicitly want userspace > to get a minor fault so it can check and potentially update the page's > contents. > > Huge PMD sharing would prevent these faults from occurring for > suitably aligned areas, so disable it upon UFFD registration. > > Reviewed-by: Peter Xu > Signed-off-by: Axel Rasmussen Thanks, Reviewed-by: Mike Kravetz -- Mike Kravetz