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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato References: <20250617154345.2494405-1-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: <20250617154345.2494405-1-david@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: iKKlWeynWjEkwsl1IGUXwJ9hptx2ylxcAz2lajo4Kus_1750177093 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: rspam03 X-Stat-Signature: jitbwyjeuq98yok6sw6w7bn48nikkgqi X-Rspam-User: X-Rspamd-Queue-Id: 5526580010 X-HE-Tag: 1750177096-624712 X-HE-Meta: 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 16CuGFD4 9ymB+KV1vv3qBsXrryY6mXdbSfYlxC91M5chlSoctQttuh20St8rsFYbqQla7Hz0bTc5TxGnXZOwy7Zcr5lzgBswrUENLEbF+Ln3Nmso8E+fQMvWv5niPmlMX6UAm9qO9vGML 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 17.06.25 17:43, David Hildenbrand wrote: > RFC because it's based on mm-new where some things might still change > around the devmap removal stuff. > > While removing support for CoW PFNMAPs is a noble goal, I am not even sure > if we can remove said support for e.g., /dev/mem that easily. > > In the end, Cow PFNMAPs are pretty simple: everything is "special" except > CoW'ed anon folios, that are "normal". > > The only complication is: how to identify such pages without pte_special(). > Because with pte_special(), it's easy. > > Well, of course, one day all architectures might support pte_special() ... > either because we added support for pte_special() or removed support for > ... these architectures from Linux. > > No need to wait for that day. Let's do some cleanups around > vm_normal_page()/vm_normal_page_pmd() and handling of the huge zero folio, > and remove the "horrible special case to handle copy-on-write behaviour" > that does questionable things in remap_pfn_range() with a VMA, simply by > > ... looking for anonymous folios in CoW PFNMAPs to identify anonymous > folios? I know, sounds crazy ;) I'll mention one corner case that just occurred to me: assume someone maps arbitrary /dev/mem that is actually used by the kernel for user space, and then some of that memory gets allocated as anonymous memory, it would probably be a problem. Hmm, I'll have to think about that, and the interaction with CONFIG_STRICT_DEVMEM. -- Cheers, David / dhildenb