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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.0 Subject: Re: [PATCH v4 4/4] selftests/hmm-tests: Add test for dirty bits To: Alistair Popple References: <9f801e9d8d830408f2ca27821f606e09aa856899.1662078528.git-series.apopple@nvidia.com> <68cf1d70f3fb8ce4e3c1a4899c19df4f6c382a13.1662078528.git-series.apopple@nvidia.com> <87mtbb5soy.fsf@nvdebian.thelocal> Content-Language: en-US From: John Hubbard In-Reply-To: <87mtbb5soy.fsf@nvdebian.thelocal> 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-TrafficTypeDiagnostic: BN8NAM11FT097:EE_|IA1PR12MB7494:EE_ X-MS-Office365-Filtering-Correlation-Id: 81a2fe45-ac9a-4885-29aa-08da911a516b 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:12.22.5.234;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:InfoNoRecords;CAT:NONE;SFS:(13230016)(4636009)(39860400002)(376002)(346002)(136003)(396003)(46966006)(36840700001)(40470700004)(40480700001)(86362001)(37006003)(356005)(31696002)(316002)(81166007)(54906003)(41300700001)(40460700003)(16576012)(478600001)(47076005)(83380400001)(2616005)(426003)(36860700001)(186003)(16526019)(336012)(6636002)(53546011)(6666004)(82740400003)(26005)(6862004)(2906002)(82310400005)(7416002)(5660300002)(36756003)(8936002)(31686004)(70206006)(4326008)(8676002)(70586007)(14143004)(36900700001)(43740500002);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Sep 2022 21:45:44.5626 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 81a2fe45-ac9a-4885-29aa-08da911a516b X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[12.22.5.234];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN8NAM11FT097.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR12MB7494 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Sierra Guiza, Alejandro \(Alex\)" , Ralph Campbell , Lyude Paul , Karol Herbst , David Hildenbrand , Nadav Amit , Felix Kuehling , linuxppc-dev@lists.ozlabs.org, LKML , Peter Xu , linux-mm@kvack.org, Logan Gunthorpe , Matthew Wilcox , Jason Gunthorpe , akpm@linux-foundation.org, huang ying , Ben Skeggs Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 9/7/22 04:13, Alistair Popple wrote: >>> + /* >>> + * Attempt to migrate memory to device, which should fail because >>> + * hopefully some pages are backed by swap storage. >>> + */ >>> + ASSERT_TRUE(hmm_migrate_sys_to_dev(self->fd, buffer, npages)); >> >> Are you really sure that you want to assert on that? Because doing so >> guarantees a test failure if and when we every upgrade the kernel to >> be able to migrate swap-backed pages. And I seem to recall that this >> current inability to migrate swap-backed pages is considered a flaw >> to be fixed, right? > > Right, that's a good point. I was using failure (ASSERT_TRUE) here as a > way of detecting that at least some pages are swap-backed, because if no > pages end up being swap-backed the test is invalid. Yes. But "invalid" or "waived" is a much different test result than "failed". > > I'm not really sure what to do about it though. It's likely the fix for Remove the assert. If the test framework allows and you prefer, you can print a warning. > swap-backed migration may make this bug impossible to hit anyway, > because the obvious fix is to just drop the pages from the swapcache > during migration which would force writeback during subsequent reclaim. > > So I'm inclined to leave this here even if it only serves to remind us > about it when we do fix migration of swap-backed pages, because we will > of course run hmm-tests before submitting that fix :-) We can then > either fix the test or drop it if we think it's no longer possible to > hit. Oh no no no, please. This is not how to do tests. If you want a TODO list somewhere, there are other ways. But tests that require maintenance when you change something are an anti-pattern. thanks, -- John Hubbard NVIDIA