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[2003:d8:2f1b:b800:6fdb:1af2:4fbd:1fdf]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-450d7f8eceasm197291125e9.7.2025.06.04.04.27.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 04 Jun 2025 04:27:52 -0700 (PDT) Message-ID: <85704ffa-6188-4b90-9455-8b9ce7b1b98e@redhat.com> Date: Wed, 4 Jun 2025 13:27:51 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC] mm: Add MADV_NONZERO to skip redundant zeroing in MADV_DONTNEED To: Harry Yoo , Ayaan Mirza Baig Cc: akpm@linux-foundation.org, linux-mm@kvack.org References: 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: sb3NB47fUgkObg4EzBp_u9B2QGQCAUm3r6OazFeVTeY_1749036473 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-Rspamd-Queue-Id: 4AE5E12000B X-Stat-Signature: u556tysnb5grb9n4wa3nkk1rb8qtzgm5 X-Rspam-User: X-HE-Tag: 1749036476-422506 X-HE-Meta: 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 2fS2FbXW KNoilYDLOcyuo6aIofU9hGvQetPKJNFoHFffVlcec0S/ij1FLrGc4APMgJLSfYn9c4iYajCDraIqvTyGJ2H5ZbVntkMID952M0FrZ8urfZr7fcrx9Qt6pzLFmZGDzu4yZvRYqXZLXZTKUdolHr5IH9qnphGbDhpGwaRl8wo3ZLoiGcXa5V9jckL06msLCTOhyHGShkWLB8uVkUjGydkGxDNyCVAasKVkKmJr4OqLL/jjpi3gV8RK40kiRsjzyOYHzfDx9H/8B5uDSjY2L9gemxtUiyxWB0qVOLnjwMas0DbPS0k1x58QxCRIUfpdReMaQ/alGzIbJU6bAh4DkjrSeCiB/eu3wOkXl3tULflbHdbOvwwJS0a/fN9Mu9XgM+H3xCX4WB3fcaGr+HZohuaot6gqJ80Yl3g0a5Po/ztFxp6sQNcTeEb4RASi5Lx8OYsx/dye8 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 04.06.25 03:49, Harry Yoo wrote: > On Wed, Jun 04, 2025 at 06:31:59AM +0530, Ayaan Mirza Baig wrote: >> Hi Andrew, >> >> I've been looking at MADV_DONTNEED and noticed we always zero pages, even >> when >> it might not be necessary for cases like: >> >> - Media buffers (video/audio processing) >> - Temporary compute workloads >> - Pre-zeroed memory pools > > Hi Ayaan, > > I don't think this "skipping zeroing" is limited to MADV_DONTNEED at all? > > We don't zero pages during zapping (unless init_on_free is enabled), > but zero pages when madvise(MADV_DONTNEED)'d area is accessed again > (for anonymous mappings), because that's how faulting anonymous mappings > works. > > And if you're suggesting that you want to skip zeroing (on some conditions) > when faulting an anonymous mapping, we can't do that because applications > rely on the guarantee that such pages are zeroed. Yeah, no way we're adding something like that. What we discussed last years at plumbers IIRC in Rik's session was having a per-process cache of zapped pages. Essentially, during MADV_DONTNEED we could move the pages to that cache, and on re-access (if the process opted in) we could grab one of these pages from the per-process cache without zeroing them out. On memory pressure we would flush the cache. There are some challenges (e.g., how to keep these pages migratable/swappable etc). -- Cheers, David / dhildenb