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Howlett" , Suren Baghdasaryan , Matthew Wilcox , Rik van Riel , Harry Yoo , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Jakub Matena , Wei Yang , Barry Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <7e51e1e2-7272-48d5-9457-40ab87ad7694@redhat.com> <76zi626uk53dtfzmezzt6cfz45ansam2gpcumddqxnipnw5jkh@qwfzoxgi255b> <68d8c7ad-aea0-4556-be63-9b67d70e4386@redhat.com> <58560256-58da-4fa6-a953-d2c4695ffba8@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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: XL1OjOw3lKJx8xOvI49EUN6yRC8_arZOz6HKcyC3raQ_1750757941 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: 99jh9444nhgyhmwqrpy4etd3rbbfqjff X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 13B6CC0004 X-HE-Tag: 1750757944-367579 X-HE-Meta: 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 W0RWogSo 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 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 20.06.25 21:28, Lorenzo Stoakes wrote: > On Fri, Jun 20, 2025 at 07:59:17PM +0100, Pedro Falcato wrote: >> On Tue, Jun 17, 2025 at 11:57:11AM +0100, Lorenzo Stoakes wrote: >>> On Tue, Jun 17, 2025 at 10:45:53AM +0200, David Hildenbrand wrote: >>>> mremap() is already an expensive operation ... so I think we need a pretty >>>> convincing case to make this configurable by the user at all for each >>>> individual mremap() invocation. >>> >>> My measurements suggest, unless you hit a very unfortunate case of -huge >>> faulted in range all mapped PTE- that the work involved is not all that >>> much more substantial in terms of order of magnitude than a normal mremap() >>> operation. >>> >> >> Could you share your measurements and/or post them on the cover letter for the >> next version? > > Yeah am going to experiment nad gather some data for the next respin and see > what might be possible. > > I will present this kind of data then. > >> >> If indeed it makes no practical difference, maybe we could try to enable it by >> default and see what happens... > > Well it makes a difference, but the question is how much it matters (we have to > traverse every single PTE for faulted-in memory vs. if we move page tables we > can potentially move at PMD granularity saving 512 traversals, but if the folios > are large then we're not really slower...). > > I have some ideas... :) As a first step, we could have some global way to enable/disable the optimization system-wide. We could then learn if there is really any workload that notices the change, while still having a way to revert to the old behavior on affected systems easily. Just a thought, I still hope we can avoid all that. Again, mremap() is not really known for being a very efficient operation. > >> >> Or: separate but maybe awful idea, but if the problem is the number of VMAs >> maybe we could try harder based on the map count? i.e if >> map_count > (max_map_count / 2), try to relocate anon. > > Interesting, though that'd make some things randomly merge and other stuff not, > and you really have to consistently do this stuff to make things mergeable. Yes, I'd prefer if we can make it more predictable. (Of course, the VMA region size could also be used as an input to a policy. e.g., small move -> much fragmentation -> merge, large move -> less fragmentation -> don't care. Knowing about the use cases that use mremap() of anon memory and how they might be affected could be very valuable. Maybe it's mostly moving a handful of pages where we most care about this optimization?). -- Cheers, David / dhildenb