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[2003:cb:c738:3100:8133:26cf:7877:94aa]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38a8e37d050sm15078092f8f.15.2025.01.14.05.01.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Jan 2025 05:01:34 -0800 (PST) Message-ID: <08e7f845-6b86-4fdc-830d-23f15ad90475@redhat.com> Date: Tue, 14 Jan 2025 14:01:32 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] /dev/zero: make private mapping full anonymous mapping To: Yang Shi , arnd@arndb.de, gregkh@linuxfoundation.org, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, vbabka@suse.cz, jannh@google.com, willy@infradead.org, liushixin2@huawei.com, akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250113223033.4054534-1-yang@os.amperecomputing.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: <20250113223033.4054534-1-yang@os.amperecomputing.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: nReC4dEjqMB0IYMZyv4OXhYffzY_nRpH2Ajj9bIUhnM_1736859696 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 2049B180011 X-Stat-Signature: 8qza49q9bqfsfqj3adpm585yuokp6a91 X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1736859698-857163 X-HE-Meta: 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 gya6Aiz6 HEFWLbDjkmmch4QyOcsH1Kgm6iq30oQecQ7f0bDyWAGS0HW3+oyGjoavv9NfbKzB5J2r36AG9hVJ+xyd4gtZu6j2HCrWZiHbxSwnapYhN272EsrLudIhHXJMbIyRLPpOK/YarUSBGeby5jRpcFk8VoI4QY/X6YHRDlO1P8x5hoLtEsd6U4sDujz5eRK4TMiY5Ja3Agy3NZW0iFT/eCCj+9wFwFdqHH9Jg30HKhNVHR9qwHQ6xT3yAJWJxFspFf3ZNa/MA1HbwW9rJoY7G5wXFOiDJGrjSR8eDjsnQFqFgh2acB4N3V9LXYJgPBPylwT+QOJtAcS1bxM5yeAi8h3U3Zx0ohajkrrzaDqqzSZaK9DKLSninf5EzKaHOqppOTdNEq9J1SuEpraUNl64= 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 13.01.25 23:30, Yang Shi wrote: > When creating private mapping for /dev/zero, the driver makes it an > anonymous mapping by calling set_vma_anonymous(). But it just sets > vm_ops to NULL, vm_file is still valid and vm_pgoff is also file offset. > > This is a special case and the VMA doesn't look like either anonymous VMA > or file VMA. It confused other kernel subsystem, for example, khugepaged [1]. > > It seems pointless to keep such special case. Making private /dev/zero> mapping a full anonymous mapping doesn't change the semantic of > /dev/zero either. > > The user visible effect is the mapping entry shown in /proc//smaps > and /proc//maps. > > Before the change: > ffffb7190000-ffffb7590000 rw-p 00001000 00:06 8 /dev/zero > > After the change: > ffffb6130000-ffffb6530000 rw-p 00000000 00:00 0 > Hm, not sure about this. It's actually quite consistent to have that output in smaps the way it is. You mapped a file at an offset, and it behaves like an anonymous mapping apart from that. Not sure if the buggy khugepaged thing is a good indicator to warrant this change. -- Cheers, David / dhildenb