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[2003:d8:2f36:d800:164f:7689:99fe:7f58]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43b73718abcsm68236435e9.22.2025.02.28.13.45.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 28 Feb 2025 13:45:58 -0800 (PST) Message-ID: Date: Fri, 28 Feb 2025 22:45:57 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/2] SKSM: Synchronous Kernel Samepage Merging To: Mathieu Desnoyers , Sean Christopherson Cc: Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org, Matthew Wilcox , Olivier Dion , linux-mm@kvack.org References: <20250228023043.83726-1-mathieu.desnoyers@efficios.com> <8524caa9-e1f6-4411-b86b-d9457ddb8007@efficios.com> <029759d4-f7b2-4ec6-b5d0-7c8a1c0fbd80@redhat.com> <331ed532-eb98-4665-9d1b-b6b8bf46e396@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: <331ed532-eb98-4665-9d1b-b6b8bf46e396@efficios.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: A_SPAYTq5ucpdFGd5Z4AgBgCskqb5esWUlmtkiFiQ7Q_1740779160 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: rspam02 X-Stat-Signature: uxi6yx6kkq77a1n6tpsph4un4mpdpr5y X-Rspamd-Queue-Id: 664B8140004 X-Rspam-User: X-HE-Tag: 1740779165-496189 X-HE-Meta: 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 hIxYaz6m pd92xwGPy4UgFKCI+jT4zHVvdg0JXQRqLj4jCbQ1cmXB+WwwyNZDHLQrp9ZgzNHRocXxtQjjAnZaa3fEDUSwG/Bbt+B7sR1mKcU0w9zV5VyyeNkb1rcJeqjWsTM6lMX8iZk1/4TBeAdO0lLSLy4b/CdRDlVxaC+f8AFWzUghnajlYPChZbkmNskQxOliTccFLcxR1Cjs1yVUZ0hr0qLOL0qQohxIn+w5G3VI7LlesNDDrzVRmw8TONA8OsySXbG22UsrYNVgecLwGnd/Lieqk5o+2MpYsCMoJ5GWHjfdUdH3++Yto/3vkfxCQwrWd+IwsktCKD20pMdMWDdvy7ncVfqiOhoPk05xMxNix9dqnHocU9iDjcQlrbYuwKk1wUwhggWn8RoorX+rBkCqCXj381oFHJaqM9f6ReaWK/M5DDvOAMNAT79YPfhZ876K/TnnAlEyeS7N69ApWIahs+VJD3FN56u4QoJrDFl5oasu5UEJjoCc= 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 22:38, Mathieu Desnoyers wrote: > On 2025-02-28 10:10, David Hildenbrand wrote: > [...] >> For example, QEMU will mark all guest memory is mergeable using MADV, to >> limit the deduplicaton to guest RAM only. >> > > On a related note, I think the madvise(2) documentation is inaccurate. > > It states: > > MADV_MERGEABLE (since Linux 2.6.32) > Enable Kernel Samepage Merging (KSM) for the pages in the range > specified by addr and length. [...] > > AFAIU, based on code review of ksm_madvise(), this is not strictly true. > > The KSM implementation enables KSM for pages in the entire vma containing the range. > So if it so happens that two mmap areas with identical protection flags are merged, > both will be considered mergeable by KSM as soon as at least one page from any of > those areas is made mergeable. I *think* it does what is documented. In madvise_vma_behavior(), ksm_madvise() will update "new_flags". Then we call madvise_update_vma() to split the VMA if required and set new_flags only on the split VMA. The handling is similar to other MADV operations that end up modifying vm_flags. If I am missing something and this is indeed broken, we should definitely write a selftest for it and fix it. -- Cheers, David / dhildenb