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Shutemov" , Vlastimil Babka , Johannes Weiner , Jonathan Corbet , Al Viro , Randy Dunlap , Kalesh Singh , Peter Xu , rppt@kernel.org, Peter Zijlstra , Catalin Marinas , vincenzo.frascino@arm.com, =?UTF-8?B?Q2hpbndlbiBDaGFuZyAo5by16Yym5paHKQ==?= , Axel Rasmussen , Andrea Arcangeli , Jann Horn , apopple@nvidia.com, Yu Zhao , Will Deacon , fenghua.yu@intel.com, thunder.leizhen@huawei.com, Hugh Dickins , feng.tang@intel.com, Jason Gunthorpe , Roman Gushchin , Thomas Gleixner , krisman@collabora.com, Chris Hyser , Peter Collingbourne , "Eric W. Biederman" , Jens Axboe , legion@kernel.org, Rolf Eike Beer , Cyrill Gorcunov , Muchun Song , Viresh Kumar , Thomas Cedeno , sashal@kernel.org, cxfcosmos@gmail.com, LKML , linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm , kernel-team References: <20211006175821.GA1941@duo.ucw.cz> <92cbfe3b-f3d1-a8e1-7eb9-bab735e782f6@rasmusvillemoes.dk> <20211007101527.GA26288@duo.ucw.cz> <202110071111.DF87B4EE3@keescook> From: John Hubbard In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SJ0PR13CA0007.namprd13.prod.outlook.com (2603:10b6:a03:2c0::12) To BY5PR12MB4130.namprd12.prod.outlook.com (2603:10b6:a03:20b::16) MIME-Version: 1.0 Received: from [10.2.57.28] (216.228.112.21) by SJ0PR13CA0007.namprd13.prod.outlook.com (2603:10b6:a03:2c0::12) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4608.5 via Frontend Transport; Thu, 7 Oct 2021 19:02:57 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 77d2aa4a-8d08-46bb-91e0-08d989c514b5 X-MS-TrafficTypeDiagnostic: BYAPR12MB2789: X-MS-Exchange-Transport-Forked: True X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:9508; 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Thanks for the clarification! >>>>>>> So, this would use filesystem as a directory for inode->name mappings. >>>>>>> One rough edge for me is that the consumer would still need to parse >>>>>>> /proc/$pid/maps and convert [anon:inode] into [anon:name] instead of >>>>>>> just dumping the content for the user. Would it be acceptable if we >>>>>>> require the ID provided by prctl() to always be a valid inode and >>>>>>> show_map_vma() would do the inode-to-filename conversion when >>>>>>> generating maps/smaps files? I know that inode->dentry is not >>>>>>> one-to-one mapping but we can simply output the first dentry name. >>>>>>> WDYT? >>>>>> >>>>>> No. You do not want to dictate any particular way of the mapping. The >>>>>> above is just one way to do that without developing any actual mapping >>>>>> yourself. You just use a filesystem for that. Kernel doesn't and >>>>>> shouldn't understand the meaning of those numbers. It has no business in >>>>>> that. >>>>>> >>>>>> In a way this would be pushing policy into the kernel. >>>>> >>>>> I can see your point. Any other ideas on how to prevent tools from >>>>> doing this id-to-name conversion themselves? >>>> >>>> I really fail to understand why you really want to prevent them from that. >>>> Really, the whole thing is just a cookie that kernel maintains for memory >>>> mappings so that two parties can understand what the meaning of that >>>> mapping is from a higher level. They both have to agree on the naming >>>> but the kernel shouldn't dictate any specific convention because the >>>> kernel _doesn't_ _care_. These things are not really anything actionable >>>> for the kernel. It is just a metadata. >>> >>> The desire is for one of these two parties to be a human who can get >>> the data and use it as is without additional conversions. >>> /proc/$pid/maps could report FD numbers instead of pathnames, which >>> could be converted to pathnames in userspace. However we do not do >>> that because pathnames are more convenient for humans to identify a >>> specific resource. Same logic applies here IMHO. >> >> Yes, please. It really seems like the folks that are interested in this >> feature want strings. (I certainly do.) For those not interested in the >> feature, it sounds like a CONFIG to keep it away would be sufficient. >> Can we just move forward with that? > > Would love to if others are ok with this. > If this doesn't get accepted, then another way forward would to continue the ideas above to their logical conclusion, and create a new file system: vma-fs. Like debug-fs and other special file systems, similar policy and motivation. Also protected by a CONFIG option. Actually this seems at least as natural as the procfs approach, especially given the nature of these strings, which feel more like dir+file names, than simple strings. thanks, -- John Hubbard NVIDIA