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Thu, 25 Aug 2022 01:26:21 +0000 Received: from BYAPR12MB3176.namprd12.prod.outlook.com ([fe80::7432:2749:aa27:722c]) by BYAPR12MB3176.namprd12.prod.outlook.com ([fe80::7432:2749:aa27:722c%7]) with mapi id 15.20.5546.022; Thu, 25 Aug 2022 01:26:21 +0000 References: <87o7wjtn2g.fsf@nvdebian.thelocal> <87tu6bbaq7.fsf@yhuang6-desk2.ccr.corp.intel.com> <1D2FB37E-831B-445E-ADDC-C1D3FF0425C1@gmail.com> <87czcyawl6.fsf@yhuang6-desk2.ccr.corp.intel.com> <874jy9aqts.fsf@yhuang6-desk2.ccr.corp.intel.com> <87czcqiecd.fsf@nvdebian.thelocal> <87o7w9f7dp.fsf@nvdebian.thelocal> User-agent: mu4e 1.6.9; emacs 27.1 From: Alistair Popple To: Peter Xu Cc: "Huang, Ying" , Nadav Amit , huang ying , Linux MM , Andrew Morton , LKML , "Sierra Guiza, Alejandro (Alex)" , Felix Kuehling , Jason Gunthorpe , John Hubbard , David Hildenbrand , Ralph Campbell , Matthew Wilcox , Karol Herbst , Lyude Paul , Ben Skeggs , Logan Gunthorpe , paulus@ozlabs.org, linuxppc-dev@lists.ozlabs.org, stable@vger.kernel.org Subject: Re: [PATCH v2 1/2] mm/migrate_device.c: Copy pte dirty bit to page Date: Thu, 25 Aug 2022 11:24:03 +1000 In-reply-to: <87o7w9f7dp.fsf@nvdebian.thelocal> Message-ID: <87k06xf70l.fsf@nvdebian.thelocal> Content-Type: text/plain X-ClientProxiedBy: SJ0PR03CA0211.namprd03.prod.outlook.com (2603:10b6:a03:39f::6) To BYAPR12MB3176.namprd12.prod.outlook.com (2603:10b6:a03:134::26) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: e12795e2-6eba-498e-22d9-08da8638d0d7 X-MS-TrafficTypeDiagnostic: MWHPR12MB1310:EE_ X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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dkim=pass header.d=Nvidia.com header.s=selector2 header.b=fjB184xZ; arc=pass ("microsoft.com:s=arcselector9901:i=1"); spf=pass (imf01.hostedemail.com: domain of apopple@nvidia.com designates 40.107.223.80 as permitted sender) smtp.mailfrom=apopple@nvidia.com; dmarc=pass (policy=reject) header.from=nvidia.com X-Rspamd-Server: rspam10 X-Stat-Signature: tmqu47mbfgonjpggcm4scp4qjqaybh59 X-HE-Tag: 1661390783-884826 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: Alistair Popple writes: > Peter Xu writes: >>> But it's kind of against a pure "optimization" in that if trylock failed, >>> we'll clear the mpfn so the src[i] will be zero at last. Then will we >>> directly give up on this page, or will we try to lock_page() again >>> somewhere? > > That comment is out dated. We used to try locking the page again but > that was removed by ab09243aa95a ("mm/migrate.c: remove > MIGRATE_PFN_LOCKED"). See > https://lkml.kernel.org/r/20211025041608.289017-1-apopple@nvidia.com > > Will post a clean-up for it. By the way it's still an optimisation because in most cases we can avoid calling try_to_migrate() and walking the rmap altogether if we install the migration entries here. But I agree the comment is misleading. >>> The future unmap op is also based on this "cpages", not "npages": >>> >>> if (args->cpages) >>> migrate_vma_unmap(args); >>> >>> So I never figured out how this code really works. It'll be great if you >>> could shed some light to it. >>> >>> Thanks, >>> >>> -- >>> Peter Xu