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Thu, 9 Sep 2021 16:50:39 +0000 Received: from BY5PR12MB4130.namprd12.prod.outlook.com ([fe80::6811:59ee:b39f:97b9]) by BY5PR12MB4130.namprd12.prod.outlook.com ([fe80::6811:59ee:b39f:97b9%9]) with mapi id 15.20.4500.016; Thu, 9 Sep 2021 16:50:39 +0000 Subject: Re: [PATCH] mm/page_isolation: don't putback unisolated page To: David Hildenbrand , Vlastimil Babka , Miaohe Lin , akpm@linux-foundation.org Cc: iamjoonsoo.kim@lge.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20210904091839.20270-1-linmiaohe@huawei.com> <3b36529f-ab97-ddfe-0407-66f0cd1fd38d@redhat.com> <2d06db75-5c26-8fe2-6883-ac99056a9894@redhat.com> <80cfffdc-227e-c045-be74-1c08fb62c1e3@redhat.com> From: John Hubbard Message-ID: <88bcab16-b248-3cdd-1270-1f162f43019f@nvidia.com> Date: Thu, 9 Sep 2021 09:50:38 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BYAPR07CA0052.namprd07.prod.outlook.com (2603:10b6:a03:60::29) To BY5PR12MB4130.namprd12.prod.outlook.com (2603:10b6:a03:20b::16) MIME-Version: 1.0 Received: from [10.2.63.205] (216.228.112.22) by BYAPR07CA0052.namprd07.prod.outlook.com (2603:10b6:a03:60::29) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4500.14 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?YXcyOGxOOUpxUlVZUlE5ZkdpZDZoK0NzMW8wRHV2a0FQUGR4dWdCOGhCaWhP?= =?utf-8?B?SW1oWU0zdmt6OTU5dnFXL01DTTJuM0J2WGJnaFBmZ2d0ZktraG04eHlXQ1hD?= =?utf-8?B?ampNNmtEeENjZC9NVSs5aEJtUWQzZmVQSUlFT3dIMFZsZ045MFdWZ3p1U2lE?= =?utf-8?B?cVo4bE5qYzBzTHlCK050ZWsrSnJXV3J0elBERHUyWDdVQUhJLzh4aWlsbk04?= =?utf-8?B?YVlkc0pDaDFtSFI4RXB0ak4vbXIwWHpEL2tFR3VYK2o3TDd4SDNzT1ZTZExJ?= =?utf-8?B?Y1gvVjY4SVZCNnlSampMTDJvV3c4djVDaXBJRXArTU9EVE5XSzE5ODhXSVQ5?= =?utf-8?B?TXJNaGM0a1laa2NiTUJsaEhlbytYVzUvd2JDN05ubVpaWk1waFRiNm0zU0xS?= =?utf-8?B?UHNXdEhCWUlORE9zZUp1N2ZvWE96Zjl4UGZjcjMvK2lRc2lyTVBMczI0bWNQ?= =?utf-8?B?VExOb3ZScDJDcE5wVTYwOXJmQ2ZUekorZElTTnJwcExibGwycmF1R1BxY0RI?= =?utf-8?B?VThmNGE1SmhjZTZrWjNUdTRVdXp4REp4bGordXkzdFJQMGdWYmRIMVV5UTU1?= =?utf-8?B?cmNRaU1xcUMyZjg4OEVmSXhPd0lwM0Q3SktTMWdUSFgvdFpSenNtY0VRdytS?= =?utf-8?B?SEMzRzh0bm5xL2RkYzlCVDY2aFo3VjJ1UzNDWTdHeFkxZWo2alFsRmZxN29v?= =?utf-8?B?bzdWU1R0N3YwN1g5TlNQQmVINC9zVm1TUFpLOGUzeGR0TXhOWmFXZUhuRnJ6?= =?utf-8?B?a010MzVTK3VhQSt1N0xCQnNtck5wdnB3TWtldUZYTTJnRGZETmllV0ljUElN?= =?utf-8?B?bGY1SEZHOTdqc2drUmQyOHRkVzRTOUViakZYZ0Y2RzFYWThlNDNJY3dOSW9z?= =?utf-8?B?NEU3aWdzc01qWnpJK0dvZEd1dDZsTis2RG12eUtoekNRS1Jnc2p4ZzBLTTJD?= =?utf-8?B?NU9MMlJhQ1VnSG9lYVZiVFlzVDd2dmNOQ3daUGhDbWNKWmEvR3B1Njhqc0lE?= =?utf-8?B?ZHh2SFlGVWVjRElVWGl3a1IwMjNyMmw0c01Pb0FIblR2U0pGa3VDRW5ibzBV?= =?utf-8?B?VHFpMUErOWhaOHo4cTZKRmlQZXJvWFNUQmdpNHg1QVZUanQ1aTBxRzJJeGQv?= =?utf-8?B?c3kva21SRWxsY3RwSFlJY1dFeEllY1ZDYXd2QnVGUzJSQVJDQXRla3BUdWd0?= =?utf-8?B?bkNySVlVRUxnRGtqT0FDSlFhY250QUxxOTRIeVdjNm9wa3B6VnJpT3VvQVhh?= =?utf-8?B?MGJDcGlBQ2UvTXkvTUxZcFNFQ1psK0FuYzlLKzllNllLUlZwZ2FUOEN0VW5X?= =?utf-8?B?S2M0R2piV2FnSTRaME5ROGtWVEZQVTdLM1FDa0pmTHEzZnd5V1RhMDFVRHlk?= =?utf-8?B?d0lvUUd2M3hyV3dlSHloQ3RwWVhYTXY3MEdnQmYvSUtabm1mRVdodUxDc0hp?= =?utf-8?B?UDkzcDU0WkRsMHlIMi9ZZDRzT0d3YlNod1E2ekVPWGlma0d2VWZNNUtuM3Fm?= =?utf-8?B?NWo1a1Frall6R2QySkRNQXYxRXppbWhDRkdOQ1pKRDllM2ZEVlQxWGlhbjE3?= =?utf-8?B?bWZyQ2c1Q1VuN2orTWJabTNRbTRNbVZzMnNpemdWaTFNcG5lbEUwNzBGMUlY?= =?utf-8?B?TDNlczRDMWhLZ2NTcjN6ZWxKc3pBWDMySEZNTEVmdjZIbW5LWFF6d1BHSWdL?= =?utf-8?B?eVI5N3Fnem5xenlXcE16SUs3dCt4aTRBUmY5S04zaThJMVhrZEFtYkVvNDd2?= =?utf-8?Q?GWiOyIMrPV2xXqYMC8e1v/rprQvYSCzuNGH7jAy?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 1afa96ad-82a8-4e10-f853-08d973b1f3e1 X-MS-Exchange-CrossTenant-AuthSource: BY5PR12MB4130.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Sep 2021 16:50:38.8958 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: vAv9LJEi6N5L23zw/y3fgGkEnJrihNiYEzcP8pIliG44acX6+Ss6dhObbOGnfRGpWOxFMbrNy/fxY7514CtaVw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR12MB4790 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/9/21 1:56 AM, David Hildenbrand wrote: > On 09.09.21 00:42, John Hubbard wrote: >> On 9/7/21 2:56 AM, David Hildenbrand wrote: >> ... >>>> If this can be handled gracefully, then I'd rather go with VM_WARN_ON. >>>> Maybe even WARN_ON_ONCE? >>>> >>> >>> I think either VM_BUG_ON() or VM_WARN_ON() -- compiling the runtime checks out -- should be good >>> enough. >>> >>> I'd just go with VM_BUG_ON(), because anybody messing with __isolate_free_page() should clearly spot >>> that we expect the current handling. But no strong opinion. >>> >> >> If in doubt, WARN*() should be preferred over BUG*(). There's a pretty long >> history of "don't kill the machine unless you have to" emails about this, let >> me dig up one...OK, maybe not the best example, but the tip of the iceberg: > > Please note the subtle difference between BUG_ON and VM_BUG_ON. We expect VM_BUG_ON to be compiled > out on any production system. So it's really only a mean to identify things that really shouldn't be > like that during debugging/testing. > Yes, but the end result is the same: it halts the system. It don't think it changes the reasoning about BUG vs WARN very much. > Using WARN... instead of VM_BUG_ON is even worse for production systems. There are distros that set > panic_on_warn, essentially converting WARN... into BUG... > This is different than BUG: panic() *prints a backtrace*, and then reboots the system. That is still awkward, but a little more debuggable. thanks, -- John Hubbard NVIDIA