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Mon, 19 Jul 2021 22:31:33 +0000 Received: from [10.2.84.248] (172.20.187.5) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Mon, 19 Jul 2021 22:30:47 +0000 Subject: Re: [PATCH v4] mm: introduce reference pages To: Peter Collingbourne , David Hildenbrand CC: Matthew Wilcox , "Kirill A . Shutemov" , Andrew Morton , "Catalin Marinas" , Evgenii Stepanov , Michal Hocko , Jann Horn , Linux ARM , Linux Memory Management List , kernel test robot , Linux API , References: <20210619092002.1791322-1-pcc@google.com> <30e92457-d540-159c-4c4e-0b8f0d2a1838@redhat.com> From: John Hubbard Message-ID: <5359583b-6acf-4db4-b036-ff1a538dced5@nvidia.com> Date: Mon, 19 Jul 2021 15:30:47 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [172.20.187.5] X-ClientProxiedBy: HQMAIL105.nvidia.com (172.20.187.12) To HQMAIL107.nvidia.com (172.20.187.13) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: a988364f-a59c-4a05-bffa-08d94b04f647 X-MS-TrafficTypeDiagnostic: BY5PR12MB5509: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:9508; 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:216.228.112.34;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:schybrid03.nvidia.com;CAT:NONE;SFS:(4636009)(39860400002)(396003)(136003)(376002)(346002)(46966006)(36840700001)(186003)(478600001)(16526019)(53546011)(2906002)(8676002)(26005)(86362001)(336012)(31696002)(426003)(4326008)(5660300002)(2616005)(8936002)(7416002)(7636003)(31686004)(110136005)(70206006)(70586007)(54906003)(36756003)(82310400003)(16576012)(36906005)(316002)(82740400003)(47076005)(356005)(36860700001)(83380400001)(43740500002);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 Jul 2021 22:31:33.1686 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: a988364f-a59c-4a05-bffa-08d94b04f647 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.34];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CO1NAM11FT048.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR12MB5509 Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=Nvidia.com header.s=selector2 header.b=rXEZto9P; spf=none (imf13.hostedemail.com: domain of jhubbard@nvidia.com has no SPF policy when checking 40.107.243.64) smtp.mailfrom=jhubbard@nvidia.com; dmarc=pass (policy=quarantine) header.from=nvidia.com X-Stat-Signature: nxe4d6hhxx8458sz3cqfrt56br1t89bo X-Rspamd-Queue-Id: 0C43D1009CB7 X-Rspamd-Server: rspam01 X-HE-Tag: 1626733894-50765 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 7/19/21 3:26 PM, Peter Collingbourne wrote: ... >>> diff --git a/include/linux/gfp.h b/include/linux/gfp.h >>> index 55b2ec1f965a..ae3c763eb9e9 100644 >>> --- a/include/linux/gfp.h >>> +++ b/include/linux/gfp.h >>> @@ -55,8 +55,9 @@ struct vm_area_struct; >>> #define ___GFP_ACCOUNT 0x400000u >>> #define ___GFP_ZEROTAGS 0x800000u >>> #define ___GFP_SKIP_KASAN_POISON 0x1000000u >>> +#define ___GFP_NOZERO 0x2000000u >> >> Oh god, please no. We've discussed this a couple of times already: >> whatever leaves the page allcoator shall be zeroed. No exceptions, not >> even for other allocators (like hugetlb). >> >> Introducing something like that to the whole system, including random >> drivers, destroys the whole purpose of the security feature. Please >> don't burry something so controversial in your patch. > > Got it -- I was unaware that this was controversial. > > Avoiding the double initialization does help a bit in benchmarks, at > least for the fully faulted case. The alternative approach that I was > thinking of was to somehow plumb the required pattern into the page > allocator (which would maintain the invariant that the pages are > initialized, but not necessarily with zeroes), but this would require > touching several layers of the allocator. I suppose that this doesn't That sounds right. > need to be done immediately though -- we can deal with the double > initialization for now and avoid it somehow in a followup. > Actually, I'd encourage going straight to the final result, in this case. It's good to see what we are going to end up with, and figure out if it's worth the trade-offs. thanks, -- John Hubbard NVIDIA