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(p200300d82f2c1e001e1e7a32e7986457.dip0.t-ipconnect.de. [2003:d8:2f2c:1e00:1e1e:7a32:e798:6457]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a56199aa52sm2613251f8f.36.2025.06.12.10.41.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 Jun 2025 10:41:48 -0700 (PDT) Message-ID: Date: Thu, 12 Jun 2025 19:41:47 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/3] mm/huge_memory: don't mark refcounted folios special in vmf_insert_folio_pud() To: Lorenzo Stoakes Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, Andrew Morton , Alistair Popple , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Dan Williams , Oscar Salvador References: <20250611120654.545963-1-david@redhat.com> <20250611120654.545963-4-david@redhat.com> <177cb5d1-4fde-4fa0-adbc-8e295fba403b@lucifer.local> <11d1ff4d-3f75-42a5-968e-8f4bad84ab78@redhat.com> <43e2b05f-c499-48c3-b8e4-a23ef5efc818@lucifer.local> 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: <43e2b05f-c499-48c3-b8e4-a23ef5efc818@lucifer.local> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 8IgTy37MbwqM-zU4MK-4vl8m_1nBM02bNPSRSNPnEJo_1749750110 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: 78D5480006 X-Stat-Signature: 4tx6kw1yyrn9dfhksuhcfn3c86x6qrpe X-Rspam-User: X-HE-Tag: 1749750112-235194 X-HE-Meta: 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 DU600UnE 4ANyfc5W5/hPT+6381mmCR4lUc+sA57rj9U7iZPZDfltuVv0xSR5ShxJs5kTPKj9bB1EE3fHI7JcJYCmqA3AVB4rRABLfOFju6+dDTYKICBX3lmvCa90IVYkKEN97v3iwxkoikGeoG1dPwZptN+MQSpZ4G1jJxwU9H6sKOXhLZ3FPCIbLHQLMZbNQ4FleugL4fKfZ6Jz4U9Rr6wxfYIZqgUwGieCMWIAhBZnkSXm4Bd11Mozfh9yQHoRRYrEqfo5HReXy7EVrsaUj9rj00wVGbktcspdN7n9/hI2UrEmvo4f8cl8gADBo8JKtpdbyyG2hZTUKBfRpOUGB2I4ZyiVl8c+zDxaPaDS0rbQS4qX/2pEmHjlQ6tCWTNwKPh6QnxRGBel78OenhH0nbn/kcLndQM+3vKc9G3shLK9cq5G38AP8WTBxwWchH5AO+jHNOfok0Dqmh6tkLJHIJ5E= 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 12.06.25 19:08, Lorenzo Stoakes wrote: > On Thu, Jun 12, 2025 at 07:00:01PM +0200, David Hildenbrand wrote: >> On 12.06.25 18:49, Lorenzo Stoakes wrote: >>> On Wed, Jun 11, 2025 at 02:06:54PM +0200, David Hildenbrand wrote: >>>> Marking PUDs that map a "normal" refcounted folios as special is >>>> against our rules documented for vm_normal_page(). >>> >>> Might be worth referring to specifically which rule. I'm guessing it's the >>> general one of special == don't touch (from vm_normal_page() comment): >>> >>> /* >>> * vm_normal_page -- This function gets the "struct page" associated with a pte. >>> * >>> * "Special" mappings do not wish to be associated with a "struct page" (either >>> * it doesn't exist, or it exists but they don't want to touch it). In this >>> * case, NULL is returned here. "Normal" mappings do have a struct page. >>> * >>> * ... >>> * >>> */ >> >> Well, yes, the one vm_normal_page() is all about ... ? :) > > Lol yes to be fair that is pretty obvious... > >> >>> >>> But don't we already violate this E.g.: >>> >>> if (vma->vm_ops && vma->vm_ops->find_special_page) >>> return vma->vm_ops->find_special_page(vma, addr); >>>> I mean this in itself perhaps means we should update this comment to say >> 'except >>> when file-backed and there is a find_special_page() hook'. >> >> I rather hope we severely break this case such that we can remove that hack. >> >> Read as in: I couldn't care less about this XEN hack, in particular, not >> documenting it. >> >> I was already wondering about hiding it behind a XEN config so not each and >> every sane user of this function has to perform this crappy-hack check. > > Yeah, I'm not a fan of generalised hooks if they can be avoided, especially ones > where you pass critical data structures like VMAs. > > It means you can, in theory, make no assumptions about what the caller does and > yeah. > > To do this for such a stupid edge case is ridiculous. Also, I am not sure if this works at all as intended. I want to look into cleaning that up ... When we inserted the page, we sure must have taken a reference, but when we inserted it we set pte_special() and ... didn't take a reference? Hmmmm > >> >> [...] >> >>>> } >>>> >>>> - entry = pud_mkhuge(pfn_t_pud(pfn, prot)); >>>> - if (pfn_t_devmap(pfn)) >>>> - entry = pud_mkdevmap(entry); >>>> - else >>>> - entry = pud_mkspecial(entry); >>>> + if (fop.is_folio) { >>>> + entry = folio_mk_pud(fop.folio, vma->vm_page_prot); >>>> + >>>> + folio_get(fop.folio); >>>> + folio_add_file_rmap_pud(fop.folio, &fop.folio->page, vma); >>>> + add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PUD_NR); >>> >>> Nit, but might be nice to abstract for PMD/PUD. >> >> Which part exactly? Likely a follow-up if it should be abstracted. > > Ah on second thoughts it doesn't matter, because you're using pud variants of > everything such that it wouldn't be worth it. > > Disregard this ;) Ah, I was already suspecting that you might have missed the sneaky _pud :) -- Cheers, David / dhildenb