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([2a01:599:901:4a65:acad:d401:ae54:edf3]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e56f64849sm43391315e9.11.2025.09.30.00.32.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 30 Sep 2025 00:32:31 -0700 (PDT) Message-ID: <02c8cf41-116d-46ab-9d40-803cc26dbbf8@redhat.com> Date: Tue, 30 Sep 2025 09:32:24 +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 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, akpm@linux-foundation.org References: <20250928045207.78546-1-lance.yang@linux.dev> <8476e9be-3f80-4d7a-9a38-f910661e61c6@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: <8476e9be-3f80-4d7a-9a38-f910661e61c6@linux.dev> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: J3BJEhS343_dDWwJC1DRTUlDIVGOpVxpLqIRJgEgOLU_1759217552 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: B01B8140002 X-Stat-Signature: r61qac84z5d7npnkrqh3um18t7praqyk X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1759217557-766435 X-HE-Meta: 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 Z4yGgNqd kKnnVqpwbZ0kZG7vxtOcxyoiYbj8usZVhlui2NQPncrqY8UhygppgwcmwL7Ip3xQhwX194P+Fy39X01pqnS8Mwx5bnB3R3+EM2+bVUieHzPAKr+47uQ+aZTE49CfSJ5JfsrUCw9Rj9OspYOID8oUClJbrGXLuJCpcd8IWqlv4lKKTA3vTiTrMwAiPo++izkKPE1tZpv05DHzJD7aFMQboR3+v1xakgm39vPM+PF/IPGbCCw2AmbAjxxRpW8C8SKzCF4sYvfU4bk7J5rfjRejw88PcC0qBL6XvBR3PSOlnbXVa7D0ImejU5FTFho1bfMcffoPZbRXe9GTBM5pMgZg4bGZfMmwwFckM2ElHV84PJPZJDKM0TQP1QNeLWfewQY9kAKCgI67NMXfCE+XuLlJdwbcsH40RUjX7I24t 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 29.09.25 12:08, Lance Yang wrote: > > > On 2025/9/29 16:25, David Hildenbrand wrote: >> 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. > > Got it. I’ll take a look when I get a chance ;) > >> >>> 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. > > Right, Indeed. > >> So I am not sure if this here is really worth fixing. Soft-dirty is not, >> and never will be false-positive free. > > Makes sense to me. It doesn’t seem worth the trouble to fix. Let’s go > ahead and drop it. Yeah, I would prefer if we can just decouple soft-dirty from dirty handling at some point. I recall I had a use case around PageAnonExclusive at some point. -- Cheers David / dhildenb