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[2003:d8:2f05:e100:526f:9b8:bd2a:2997]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-40fb72facf9sm17612699f8f.13.2025.09.29.01.25.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 29 Sep 2025 01:25:05 -0700 (PDT) Message-ID: Date: Mon, 29 Sep 2025 10:25:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm/ksm: fix spurious soft-dirty bit on zero-filled page merging To: Lance Yang , akpm@linux-foundation.org Cc: xu.xin16@zte.com.cn, chengming.zhou@linux.dev, ran.xiaokai@zte.com.cn, yang.yang29@zte.com.cn, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ioworker0@gmail.com References: <20250928045207.78546-1-lance.yang@linux.dev> 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20250928045207.78546-1-lance.yang@linux.dev> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: fR6uyfR1dNlgs3LVajx3lwaXLJY5e4amjoB98fWuZQ8_1759134306 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-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 743E040004 X-Stat-Signature: uu38oe17nxeobf83kg7ygkgj1uto9j81 X-HE-Tag: 1759134309-360369 X-HE-Meta: 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 4S3gCXlR jjhe4TzDDNJ88LetgLRiqtTwel52OqCvTgRYUZMWhuYT9bAQ= 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 28.09.25 06:52, Lance Yang wrote: > From: Lance Yang > > When KSM merges a zero-filled page with the shared zeropage, it uses > pte_mkdirty() to mark the new PTE for internal accounting. However, > pte_mkdirty() unconditionally sets both the hardware dirty bit and the > soft-dirty bit. > Right, that's one think we should clean up at one point. > This behavior causes false positives in userspace tools like CRIU that > rely on the soft-dirty mechanism for tracking memory changes. IIRC, false positives are not a problem. We get them all of the time when merging VMAs etc. So I am not sure if this here is really worth fixing. Soft-dirty is not, and never will be false-positive free. -- Cheers David / dhildenb