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([2a02:8070:4688:86a0::a40b]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-390e47a7868sm5548287f8f.24.2025.02.28.07.34.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 28 Feb 2025 07:34:51 -0800 (PST) Message-ID: Date: Fri, 28 Feb 2025 16:34:50 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/2] SKSM: Synchronous Kernel Samepage Merging To: Linus Torvalds , Mathieu Desnoyers Cc: Andrew Morton , linux-kernel@vger.kernel.org, Matthew Wilcox , Olivier Dion , linux-mm@kvack.org References: <20250228023043.83726-1-mathieu.desnoyers@efficios.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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: JAusAarlgj2UQ79nuhf-ld63LC1TkePJ3Q-N5O0wats_1740756892 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: q79q1b3suxbihdm4rsaxxbj8zozfxaty X-Rspamd-Queue-Id: 0402940005 X-Rspamd-Server: rspam07 X-HE-Tag: 1740756896-827189 X-HE-Meta: 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 oMTIC125 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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 28.02.25 03:51, Linus Torvalds wrote: > On Thu, 27 Feb 2025 at 18:31, Mathieu Desnoyers > wrote: >> >> This series introduces SKSM, a new page deduplication ABI, >> aiming to fix the limitations inherent to the KSM ABI. > > So I'm not interested in seeing *another* KSM version. > > Because I absolutely do *NOT* want a new chapter in the saga of SLUB > vs SLAB vs SLOB. > > However, if the feeling is that this can *replace* the current horror > that is KSM, I'm a lot more interested. I suspect our current KSM > model has largely been a failure, and this might be "good enough". Maybe it would be comparable to khugepaged vs. MADV_COLLAPSE? Many/most use cases just leave THP scanning+collapsing to khugepaged; selected ones might "know better" what to do, so they effectively disable khugepaged, and manually collapse THPs using MADV_COLLAPSE. If it would be similar to that, it would not be completely different KSM version, just a different way to trigger merging: background scanning vs. user-space triggered ("synchronous"). I could see use cases for such a synchronous interface, but I doubt it could replace the background scanning that is actively getting used for existing use cases; I have similar thoughts about khugepaged vs. MADV_COLLAPSE. -- Cheers, David / dhildenb