From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 68C3A44BC9B; Fri, 27 Feb 2026 20:10:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772223057; cv=none; b=ahRU4XnUqYyoihqzo5vDQsc/bGchv69NvPRu+b85b84DsSYwXK2/SmIur+8jTbWXAzU2kZH3kz4jaBXwouvTRgBl4QuuE7PK5ek8/M6ZZK8lMx9WsF7fJLn5h07QQmbzT86emXhf+VEcYj95L+mZDUtHjsj5UZVEs1jNTVjf65M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772223057; c=relaxed/simple; bh=jawrG5lIlf8r9SGf1ieHXs/Tuz45v8rDUPxryvUaV8E=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=meo3hxjSzCR5IX1+wtZfJXd03qo6QucnCLb0QqHkdHTBfrr/dFKMq05yaH93pX2Dr/Fwzq10Kqz1gpjjyR2yj6kVo3UA3BHROfDfnZv4RTWtI2cptnpryub9IhMHgslGOhBMLXTeqjM32qYcee91ssa9wh7QXB75alfYu5ZwlVg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=d/HFL0Fk; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="d/HFL0Fk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9D22CC116C6; Fri, 27 Feb 2026 20:10:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772223057; bh=jawrG5lIlf8r9SGf1ieHXs/Tuz45v8rDUPxryvUaV8E=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=d/HFL0FkqT8KhCLXzaDSkrS9rHD9axeGLaqpM2O67n2P3LKNFSmwD6SH63T0jut9Z SK1d6slkBbnnH2VHeYh1vteg1E8x14NbMcGuOJ+TvD8PkNEI/vJ5Pd8+h1nJeFerI0 DKhUbCQ+BKYwmyKAfcUHVAwBa9rtKfItEbpRo2fxi7l03iyp/4gIts9hzskfDzAmyb V2nnVISbac74ngfir65upc/wTcH2wk6RydaF96Ig04XwXFAErwdhzWxbcoAa8A1Bnt NLMlr1920Rz5scR5uepF/JhaHSGFx2so4XrbNN+RtjEBeHk1zwk3WNW5UOOWAStdCZ reLXXJgjhiaMg== Message-ID: <653e34d4-6356-4f9e-8298-40b4e237f761@kernel.org> Date: Fri, 27 Feb 2026 21:10:49 +0100 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC v2 0/3] Decoupling large folios dependency on THP To: Matthew Wilcox Cc: Pankaj Raghav , Suren Baghdasaryan , Mike Rapoport , Ryan Roberts , Michal Hocko , Lance Yang , Lorenzo Stoakes , Baolin Wang , Dev Jain , Barry Song , Andrew Morton , Nico Pache , Zi Yan , Vlastimil Babka , "Liam R . 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 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