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[2003:cb:c745:a500:7f54:d66b:cf40:8ee9]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a073e5bc8bsm17668519f8f.81.2025.04.30.14.36.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 30 Apr 2025 14:36:55 -0700 (PDT) Message-ID: <77adaca4-fef3-4a5d-9dc7-a0e8d41eaf4c@redhat.com> Date: Wed, 30 Apr 2025 23:36:55 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC Patch 0/5] Make anon_vma operations testable To: Wei Yang Cc: Lorenzo Stoakes , akpm@linux-foundation.org, riel@surriel.com, vbabka@suse.cz, harry.yoo@oracle.com, jannh@google.com, baohua@kernel.org, linux-mm@kvack.org References: <20250429090639.784-1-richard.weiyang@gmail.com> <8c268ece-71a7-470a-bf8b-71d3e4920977@redhat.com> <20250429235608.yvbcxybkfsmp6ow5@master> <20250430154406.aadkqzguil2zafq5@master> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20250430154406.aadkqzguil2zafq5@master> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: BdScIjObkXwp1wm8u5C5vyhwqLsAZUetA95_RSyBj6w_1746049017 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: ozhn3tgwjkozkwd6utc5zbyzu1mhdss3 X-Rspamd-Queue-Id: B7D4880007 X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1746049019-34772 X-HE-Meta: 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 KzyQHXLS 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 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: List-Subscribe: List-Unsubscribe: On 30.04.25 17:44, Wei Yang wrote: > On Wed, Apr 30, 2025 at 09:47:16AM +0200, David Hildenbrand wrote: >> On 30.04.25 01:56, Wei Yang wrote: >>> On Tue, Apr 29, 2025 at 10:41:27AM +0100, Lorenzo Stoakes wrote: >>>> On Tue, Apr 29, 2025 at 11:38:23AM +0200, David Hildenbrand wrote: >>>>> On 29.04.25 11:31, Lorenzo Stoakes wrote: >>>>>> Wei, >>>>>> >>>>>> NACK the whole series. >>>>>> >>>>>> I'm really not sure how to get through to you. You were _explicitly_ >>>>>> advised not to send this series. And yet you've sent it anyway. >>>>>> >>>>>> I mean, I appreciate your enthusiasm and the fact you've made tests here >>>>>> etc. obviously. And you've clearly put a TON of work in. But I just don't >>>>>> know why you would when explicitly told not to without at least discussing >>>>>> it first? >>>>>> >>>>>> This just isn't a great way of interacting with the community. We're all >>>>>> human, please try to have some empathy for others here, as I really do try >>>>>> to have with you as best I can. >>>>>> >>>>>> This adds a ton of churn and LOCKS IN assumptions about how anon_vma works, >>>>>> clashes with other series (most notably series I've been working on), takes >>>>>> away from efforts I want to make to start to join file-backed and anon >>>>>> reverse mapping logic, separates the two in such a way as to encourage this >>>>>> to nonly grow and generally isn't conducive to where I want to go with >>>>>> rmap. >>>>> >>>>> anon_vma, the unloved child. :) >>>>> >>>>> I would love to see a simplification that makes it less special, and I can >>>>> understand how adding tests for the ways it is special can be >>>>> counter-productive. >>>>> >>>>>> >>>>>> This is part of why I explicitly told you please don't go down this road, >>>>>> because you're likely to end up doing work that doesn't get used. It's not >>>>>> a great use of your time either. >>>>>> >>>>>> Since there's something useful here in tests, I may at a later date come >>>>>> back to those. >>>>> >>>>> Agreed, skimming over the tests there are some nice diagrams and cases. >>>>> >>>>> But I would hope that for most of these cases we could test on a higher >>>>> level: test our expectations when running real programs that we want to >>>>> check, especially when performing internal changes on how we handle anon >>>>> memory + rmap. >>>>> >>>>> E.g., do fork(), then test if we can successfully perform rmap >>>>> lookups/updates (e.g., migrate folio to a different numa node etc). >>>>> >>>> >>>> That's a great point! Wei - if you could look at making some self-tests >>>> (i.e. that live in tools/testing/selftests/mm) that try to recreate _real_ >>>> scenarios that use the rmap like this and assert correct behaviour there, >>>> that could be a positive way of moving forward with this. >>>> >>> >>> I am trying to understand what scenarios you want. >> >> That is exactly the task to figure out: how can we actually test our rmap >> implementation from a higher level. The example regarding fork and migration >> is possibly a low-hanging fruit. >> >> We might already have the functionality to achieve it, *maybe* we'd even want >> some extensions to make it all even easier to test. >> >> For example, MADV_PAGEOUT is refused on folios that are mapped into multiple >> processes. Maybe we'd want the option to *still* page it out, just like >> MPOL_MF_MOVE_ALL allows with CAP_SYS_NICE to *still* migrate a folio that is >> mapped into multiple processes. >> >> Some rmap tests could make sense for both, anon and pagecache folios. >> >>> >>> Something like below? >>> >>> * fork and migrate a range in child >>> * fork/unmap in parent and migrate a range in child >>> >>> If the operation is successful, then we are good, right? >> >> Yes. And one can come up with a bunch of similar rmap test cases, like doing >> a partial mremap() of a THP, then testing if the rmap walk still works as >> expected, pairing the whole thing with for etc. >> >> One "problem" here is that even with MPOL_MF_MOVE_ALL, >> move_pages() will not move a folio if it already resides on the target node. >> So one always needs two NUMA nodes, which is a bit suboptimal for testing >> purposes. >> >> For testing purposes, it could have been helpful a couple of times already to >> just have a way of migrating a folio even if it already resides on the >> expected node. >> > > Thanks for all those detail explanation. I need some time to digest it. > > Since lack of some background knowledge, I may have further questions on this. > Hope won't bother you too much. Sure, feel free to reach out. Having more selftests that test rmap behavior could be really helpful. -- Cheers, David / dhildenb