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Howlett" , Jens Axboe , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, mcgrof@kernel.org, gost.dev@samsung.com, kernel@pankajraghav.com, tytso@mit.edu References: <20251206030858.1418814-1-p.raghav@samsung.com> <8ca84535-861c-4ab0-a46b-5dfe319ac8ac@kernel.org> 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-Rspamd-Queue-Id: 0D33D16000F X-Stat-Signature: w6xyuq1p86hwywynw5i7twk13scu4cnx X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1772223057-535415 X-HE-Meta: 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 FzuprW+k jrWU/Ijd53QaucT+g6Pf6R3m4xCd9JM66RjGe4cHv2xdPu/XL9UBuZl++J2Vp+E7/8vvOiBfHEy8kD8ZQ8w5EL7/lfYa1RO4VTl2t954xukImB0xb97tRw6oeX1sOw8z5dni/VjoZ/Hd2nM9RkQKINB997QRUCZghT0djeS25sFG8GZeICADnz2KC3DicDzsWUnBnrIyJAQGfO4dzl30WsUbqSP5wp2YJFabRUWfE9ivOn+OnrNqrPNcLuupNktHSB/Kn Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/27/26 16:19, Matthew Wilcox wrote: > On Fri, Feb 27, 2026 at 09:45:07AM +0100, David Hildenbrand (Arm) wrote: >> I guess it would be rather trivial to just replace >> add_to_page_cache_lru() by filemap_add_folio() in below code. > > In the Ottawa interpretation, that's true, but I'd prefer not to revisit > this code when transitioning to the New York interpretation. This is > the NOMMU code after all, and the less time we spend on it, the better. > >>> So either we need to reimplement all the good stuff that folio_split() >>> does for us, or we need to make folio_split() available on nommu. >> >> folio splitting usually involves unmapping pages, which is rather >> cumbersome on nommu ;) So we'd have to think about that and the >> implications. > > Depending on your point of view, either everything is mapped on nommu, > or nothing is mapped ;-) In any case, the folio is freshly-allocated > and locked, so there's no chance anybody has mapped it yet. > >> ramfs_nommu_expand_for_mapping() is all about allocating memory, not >> splitting something that might already in use somewhere. >> >> So I folio_split() on nommu is a bit weird in that context. > > Well, it is, but it's also exactly what we need to do -- frees folios > which are now entirely beyond i_size. And it's code that's also used on > MMU systems, and the more code that's shared, the better. > >> When it comes to allocating memory, I would assume that it would be >> better (and faster!) to >> >> a) allocate a frozen high-order page >> >> b) Create the (large) folios directly on chunks of the frozen page, and >> add them through filemap_add_folio(). >> >> We'd have a function that consumes a suitable page range and turns it >> into a folio (later allocates memdesc). >> >> c) Return all unused frozen bits to the page allocator > > Right, we could do that. But that's more code and special code in the > nommu codebase. I guess I'd have to see the frankenstein folio_split() to judge if it is really better :) If it's really just about skipping the unmap+remap the end result would indeed be nice. -- Cheers, David