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[2003:cb:c708:1d00:99ec:9656:7475:678d]) by smtp.gmail.com with ESMTPSA id do4-20020a0560000c4400b00332f2288e2esm10265166wrb.102.2023.11.28.09.42.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Nov 2023 09:42:45 -0800 (PST) Message-ID: Date: Tue, 28 Nov 2023 18:42:44 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 2/5] mm/rmap: introduce and use hugetlb_remove_rmap() To: Peter Xu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Mike Kravetz , Muchun Song References: <20231128145205.215026-1-david@redhat.com> <20231128145205.215026-3-david@redhat.com> 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: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: C927640004 X-Stat-Signature: df7hjrz37ea8p7mti3gk59w13bdibpnt X-Rspam-User: X-HE-Tag: 1701193369-86467 X-HE-Meta: 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 wPXc3/dF vI0W1n7lpl1LMeLJEG02IxGgX7B1/g+YLamHWWZDGeoxE1BMSYGORwhsxYYdwQH49Z1ChX7ugxZwVCf4IpfxKH8ptzFlzTp6QdY9S/wZI8FbdSj+fmr4WpRMqC0O51LoGDFWn7Lb+ejHrVPQVAC9yz8vtAWWZPZOOOZC1tDPcqVUR++o3+gdI1hwOodBpHEo0/P0AMKJQLBqKOZ7yqdPPRo42/IgC26N+h9+m97yKHCGOrdTgK8AtliwZ5W4OK/wJi9/L5g/aXPwfVmoA2UC4HMIgPegE0phnVEaW+8AJ04uGzhvrJ4NWKgP8AYgyYP9TJwVEzdCxqwg7b07daeyiH1tjupd4XxArrOOM+xXe6bTBSyTXhtiOtrWpL9NmBcosiafm7i6VWmHjpuSW1C8QxIxgTbWIo/sXw1I4K77Rsuw2m/ruZj978rheDyiQj94B1pLt0T6O70readaDFlkEDJ84lQ== 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 28.11.23 18:13, Peter Xu wrote: > On Tue, Nov 28, 2023 at 05:39:35PM +0100, David Hildenbrand wrote: >> Quoting from the cover letter: >> >> "We have hugetlb special-casing/checks in the callers in all cases either >> way already in place: it doesn't make too much sense to call generic-looking >> functions that end up doing hugetlb specific things from hugetlb >> special-cases." > > I'll take this one as an example: I think one goal (of my understanding of > the mm community) is to make the generic looking functions keep being > generic, dropping any function named as "*hugetlb*" if possible one day > within that generic implementation. I said that in my previous reply. Yes, and I am one of the people asking for that. However, only where it makes sense (e.g., like page table walking, GUP as you said), and only when it is actually unified. I don't think that rmap handling or fault handling will ever be completely unified to that extreme, and it might also not be desirable. Just like we have separate paths for anon and file in areas where they are reasonable different. What doesn't make sense is using patterns like: page_remove_rmap(subpage, vma, folio_test_hugetlb(folio)); and then, inside page_remove_rmap() have an initial folio_test_hugetlb() check that does something completely different. So each and everyone calling page_remove_rmap (and knowing that it's certainly not a hugetlb folio) has to run through that check. Then, we have functions like page_add_file_rmap() that look like they can be used for hugetlb, but hugetlb is smart enough and only calls page_dup_file_rmap(), because it doesn't want to touch any file/anon counters. And to handle that we would have to add folio_test_hugetlb() inside there, which adds the same as above, trying to unify without unifying. Once we're in the area of folio_add_file_rmap_range(), it all stops making sense, because there is no way we could possibly partially map a folio today. (and if we can in the future, we might still want separate handling, because most caller know with which pages they are dealing, below) Last but not least, it's all inconsistent right now with hugetlb_add_anon_rmap()/hugetlb_add_new_anon_rmap() being there because they differ reasonably well from the "ordinary" counterparts. > > Having that "*hugetlb*" code already in the code base may or may not be a > good reason to further move it upward the stack. If you see a path forward in the foreseeable future where we would have code that doesn't special-case hugetlb in rmap calling code already, I'd be interested in that. hugetlb.c knows that it's dealing with hugetlb pages. huge_memory.c knows that it's dealing with PMD-mapped thp. memory.c knows that it it's dealing with PTE-mapped thp or small folios. Only migrate.c (and e.g., try_to_unmap()) in rmap.c handle different types. But there is plenty of hugetlb special-casing in there that I don't really see going away. > > Strong feelings? No, I don't have. I'm not knowledged enough to do so. I'm sure you are, so I'm trusting your judgment :) I don't think going in the other direction and e.g., removing hugetlb_add_anon_rmap / hugetlb_add_new_anon_rmap is making a unification that is not really reasonable. It will only make things slower and the individual functions more complicated. -- Cheers, David / dhildenb