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[2003:d8:2f3f:f800:c101:5c9f:3bc9:3d08]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e33105e0bsm14956875e9.5.2025.09.25.03.37.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Sep 2025 03:37:43 -0700 (PDT) Message-ID: <462bb4e3-7a38-4155-9f95-52fbb4b6d464@redhat.com> Date: Thu, 25 Sep 2025 12:37:42 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: move rmap of mTHP upon CoW reuse To: Dev Jain , akpm@linux-foundation.org Cc: lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Lokesh Gidra References: <20250925085429.41607-1-dev.jain@arm.com> <072b8684-47fe-4a2a-bf69-f6d348f0489b@redhat.com> <45e08ee0-c85e-469e-a3eb-4ca2e8b7ec0c@arm.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 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: <45e08ee0-c85e-469e-a3eb-4ca2e8b7ec0c@arm.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: qcPYll9UUZ5-5sQ_VKqx0KUPB5PB1Y1XlBp5vnq4ozQ_1758796665 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: ihpsma1fgdfa87jcuxu6x7dqgncpi8x8 X-Rspam-User: X-Rspamd-Queue-Id: C8E93A0002 X-Rspamd-Server: rspam10 X-HE-Tag: 1758796669-936281 X-HE-Meta: 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 h9eEsKdF WZW1AWXnETd+NtYyY7ZovlOP0VInrAGwT8ai6ZJDjwGXzU3622YFqb6CP6yO5E546u6VmxiiGyQqGlKSeuAsQEKi796S3fWKVuUmw81uiErqZADLbrb2GgL+XnJX+zq2BKuZr9oW+rL59wqLsEbNOb4kdjMx6iKF63mQ0/Ba23+IV7OUe7WB7VGHT1V3jyEDLUcQZIAtVpIIuJ1aKy23To1EH/mdF9RKroIkaTbVlwklqvpnlbh32+D+LfC4Ph0sjgp+fViWjAhtgWHRqpVSA//3zqP6eDjPi+afBtdWen+3hXHh8+9vVTrZjcMblwB1CbrDe1CHCN1gKg3UUMAXUSoxz8T2m/DOE3WaA7aUjjA/bfmrSY5tW7KAjFkbtbaZzLpdqyq9CjXe+WIoRSpUfI2OfRlWRDf53W49U2ba6D5GUkM6UEejzqAorWQ== 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 25.09.25 12:33, Dev Jain wrote: > > On 25/09/25 2:46 pm, David Hildenbrand wrote: >> On 25.09.25 10:54, Dev Jain wrote: >>> At wp-fault time, when we find that a folio is exclusively mapped, we >>> move >>> folio->mapping to the faulting VMA's anon_vma, so that rmap overhead >>> reduces. This is currently done for small folios (base pages) and >>> PMD-mapped THPs. Do this for mTHP too. >> >> I deliberately didn't add this back then because I was not able to >> convince myself easily that it is ok in all corner cases. So this >> needs some thought. > > Thanks for your detailed reply. > > >> >> >> We know that the folio is exclusively mapped to a single MM and that >> there are no unexpected references from others (GUP pins, whatsoever). >> >> But a large folio might be >> >> (a) mapped into multiple VMAs (e.g., partial mprotect()) in the same MM > > I think we have the same problem then for PMD-THPs? I see that > vma_adjust_trans_huge() only does a PMD split and not folio split. Sure, we can end up in this reuse function here for any large anon folio, including PMD ones after a PMD->PTE remapping. -- Cheers David / dhildenb