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[2003:cb:c73b:ba00:bcff:e7c1:84bd:9486]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-434aa7e5285sm187801005e9.40.2024.12.02.07.40.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Dec 2024 07:40:30 -0800 (PST) Message-ID: <795a454b-a432-4200-8524-003e5ad53d03@redhat.com> Date: Mon, 2 Dec 2024 16:40:30 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [QUESTION] Resizing shared mapping without clashing with others To: Dmitry Dolgov <9erthalion6@gmail.com> Cc: linux-mm@kvack.org References: <3kpxpd3dbjgg6epasi2554c4qyils4t3cm2pjnyzer7gkyoaxl@khhdxjiggyhp> 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-MFC-PROC-ID: M6H5PqgeIsxzdagk_jUQgSqCAcG_Jo9FzyfM0RZe6lg_1733154032 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: 1A7804001B X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: 66hgad69zb59oijizifc57s5mbjbc1gp X-HE-Tag: 1733154019-873128 X-HE-Meta: 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 kYxd+fhS oPSm4NlRsWdNAyqLlXmC5ILZi7ExW81URUNyIGfPgTyyyoGzQdl7oAGIo9j2uTepvpaLQX1L3Dt2NHCP6OPjV9C6QckFK/r1tPxlw5bajfPfROlZVL2B5FkbDHUDmaW51lDl7Q3iT3u0kaRZZD9/wcf4LjVTa/k+PdW3MxkA/qy3dx+D81XSL60ahm+4Rc2a3lqL7pf7c9c3OpPxg4tHmkjFbV/N5BBc0wgCmlCTBSBXRPLAbpyhlUmlxYmkHPiBgiXS39o3omwuljgsNgDMVVe62dlVLMT+rsmLfQkOcx2Q67QmbYE6G96ODnBGslvUNkzxK2qC2iD5O5+74KpKHkD5XyC4rkANEb5NnBBugS/ibyTGzDWNxeFqaET5NF9NVd5ZeMrcRwt0oo5c= 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 02.12.24 16:04, Dmitry Dolgov wrote: >> On Mon, Dec 02, 2024 at 12:07:01PM GMT, David Hildenbrand wrote: >> >> Likely it's best to look into reserving a large VMA space using >> mmap(MAP_PRIVATE|MA_ANON, PROT_NONE); it's reserved but inaccessible, so it >> cannot get reallocated for different purposes. Then converting pieces of >> that into actually usable shared anonymous memory (e.g., MAP_FIXED). > > Yes, we've considered this option, preparing an initial "reserving" > mapping, then take pieces out of it for usage. As I've mentioned to > Matthew, there seems to be arguments against this approach. In a few > words: Note that this approach is extremely common ;) > > * The impact on OOM decisions is not clear (at least to me). There are none. mmap(MAP_PRIVATE|MAP_ANON, PROT_NONE) will neither allocate memory/page tables nor commit memory. > * In certain cases this will be counted against a reservation limits, > although we don't use the memory yet (e.g. with hugetlb insige a > cgroup with hugetlb.2MB.rsvd.limit_in_bytes set). With mmap(MAP_PRIVATE|MAP_ANON, PROT_NONE)? Unlikely. In any case, you might be able to tame reservations using MAP_NORESERVE. -- Cheers, David / dhildenb