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[2003:d8:2f09:9c00:8173:2a94:640d:dd31]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45b6f0c6b99sm314145815e9.4.2025.09.03.02.38.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 03 Sep 2025 02:38:52 -0700 (PDT) Message-ID: Date: Wed, 3 Sep 2025 11:38:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Where to put page->memdesc initially To: Matthew Wilcox , Jason Gunthorpe Cc: linux-mm@kvack.org References: <20250902211514.GQ186519@nvidia.com> <20250902235740.GD470103@nvidia.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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 7huhhJjlz5KIBr5k9Kg4DBhvpXeT5Gs15Neit5_qDrc_1756892334 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 46C5240002 X-Rspamd-Server: rspam04 X-Rspam-User: X-Stat-Signature: jkdfyfb8di183phfsjy5g1ua9r5nxxkb X-HE-Tag: 1756892337-987767 X-HE-Meta: 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 +DtzuQcp cxYCrKiRfCfN8RArYMwe88BR67r1TRLp2SO9NsdCROmgVXldgT99bSX9ghULbRv0JqBxE/OVJrKOxgiZ1brjAHHyV1Mr2zL0tRpeEADrZIBH9hMjl4W32K97mUfkY93Yy08Nv8e4tZRsRJixUkNPiIjYKNX9wApAnO2WJZio2cShVQQIsYxn0D3GRb1m7UVQEclRrKTFTb/4M4ybxk/DSmIGXf8uQOS5gavY2YvOGpCWtZZIKoXPbRIXp/8c36WXLAU/DaN1zcLiwACQBg+zhw8xc/lvS+uCmzFTtECOnlAeD5CZN+Q9dIcsibFTTuvBIxZpuo4mQVMo408YaOJl8lX43EuPe+/3onC5sy0ialrqYKIyyQpUJjA54E7xhy/QxpOesfiHawmBTRe4Lx07qiS6lFVETVw3bPkmX2gHouP5rsbE= 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: >> It is the same as GUP fast does for the PTE today. So this would now >> recheck the PTE and the memdesc. > > Ah, yes, I missed the step where we recheck the PTE. Thanks. > >> This recheck is because GUP fast effectively runs under a >> SLAB_TYPESAFE_BY_RCU type of behavior for the struct folio. I think >> the memdesc would also need to follow a SLAB_TYPESAFE_BY_RCU design as >> well. > > I haven't quite figured out if _all_ memdescs need to be TYPESAFE_BY_RCU > or only the ones which either have refcounts or are otherwise > migratable. Slab should be safe to be not TYPESAFE because if we ever > see a PageSlab, we won't try to dereference the pointer in GUP, > pagecache lookup or migration. I need to look through David's recent > patches again to understand how migration is going to work (obviously > we won't try to migrate slab pages). The long term plan is to work on frozen pages (with balloon pages that's easy, with zsmalloc I am not sure yet). Migration core will be responsible for freeing these frozen pages after migration succeeded etc. PageOffline pages won't allocate any memdesc. Zsmalloc will have to allocate one. I would expect that the ->migrate_page() callback will just get a frozen page and the callback will figure out what to do in regards of the medesc. It's going to be a bunch of work and I am getting interrupted working on it ... -- Cheers David / dhildenb