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Peter Anvin" , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jonas Bonn , Stefan Kristiansson , Stafford Horne , linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-openrisc@vger.kernel.org References: <20260722-dummy_ptxp3-v2-0-d9e4bad31e0a@arm.com> <0143b927-08c5-4e94-ae6e-2a0d7bfe950f@intel.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 0FBC01C0007 X-Stat-Signature: 3srxjn4whmbzayiwumtmdrucwkun9k39 X-HE-Tag: 1785165497-968593 X-HE-Meta: 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 xtV8SbFi nUUv1wIOph5wYdAHs8md1Pun0wKYywsNI1SZkU46adDs5Z6wgbN5s3wwbsQZrgoCsFPlLLP287qsvabSUP60AV4WxHXmc/vNiGC2x2E/ZzkrJOF2KAPlEDeEgeggB9li7mUgZY8o5baT/kgWcyf56TUAGi2YBYEYoaqCfqyZocZyZkN0N4MIZTVTIDhKkkHOACYw0HZtYSzanvyFW+9lcfmlkF1ZxOgus5wPc7ZqhzbK5LH19aXvkE8dX7ioZjI8nPBpAwjnn66gTIdQxMbwVXNsgxRBt5Abo6Exl/kx85+pQwBfwOHgT2rDZFQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/22/26 19:30, Yeoreum Yun wrote: >> One of my nits about v1 was that it didn't really frame the series >> precisely. It talks about "optimization" instead of fundamentally >> changing the way that the kernel deals with folded page table levels. >> >> The optimization that this *wants* to talk about kinda falls out of that >> refactoring. It's not really the core of the series, IMNHO. >> >> This series effectively changes the rules about where and how folded >> page table levels can be manipulated. In doing that, the door is opened >> to optimizing out the unnecessary loads. > > I see. might the title and the cover letter should be reparsed. > Thanks to remind it again :) While v1 changed "where and how folded page table levels can be manipulated" more drastically, v2 leaves most of set_pgd/... working for now, and really only changes how pgd_get() operates. With v2, there is mostly only a change for page table walkers that use pgd_get(): while the existing model already made all these levels be skipped in most places except in ptdump code, we now also have to skip them in ptdump code. So yes, that should be clearly spelled out: as long as pgd_get() is not involved, set_pgd()/pgd_page_vaddr()... will keep working as is. The moment someone switches to pgd_get() with folded page tables (like riscv already does), set_pgd() is disallowed, and modifications on the actual level must be performed. As discussed, a common helper for vmalloc faults would already minimize the pain quite a lot in that scenario. While we should make that clearer in the patch description, I am wondering whether we should also add some basic MM documentation for folded page tables, where we at least explain the current state-of-the-art (what's ignored when traversing, why does "no_p4d" actually mean "pgd helpers are dummies and p4d helpers implement the real logic"). -- Cheers, David