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 C1D7A389E08; Fri, 27 Feb 2026 08:45:16 +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=1772181916; cv=none; b=VQkW1Ychr5+iof5Ex+ALSCBg76ZdLqTZyHg8Ut9pRTvVbOMycpWtD+n8aSLhBcUShnTtl391XjFB1XpxsJYtiM2cVlqNWnUGzwf9QtmC4sCzzZbSFXBCFrqO59z3C5Nmb2NW8F0D7HyePwFw7kv2w5YxlK9362a9XXMzlLEPEow= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772181916; c=relaxed/simple; bh=M3wiUV92iKKp8CgWC8J6GoLftiC/em8BQZ0MsIGSMhk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=iw2g68lsmk6PnX4jcTPFJnMrtyUGcWR4SuxaWOYCgaCYfz22hSRHU86/e1GxnkPxQWZn4D/T0qf9h298k+jFBd7PrI8hYr/Sdw7PO+WbfrpLflJOVni+Pb5Z92swwvDV29UBDFCaV315a8KXVxLdrRsGgadiQ2y3l4DgqwLkQZI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lEGAfAq9; 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="lEGAfAq9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CBE0BC116C6; Fri, 27 Feb 2026 08:45:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772181916; bh=M3wiUV92iKKp8CgWC8J6GoLftiC/em8BQZ0MsIGSMhk=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=lEGAfAq935TU0KRtBBEWHVxzGrMa5zoqShGP8N9yO5S9/gmcV2y+tC+Tz0zPyvBNy 3cQyjoyFvIFs1738k5ViVxk6RttUCy2/yS2qC772eQRbRI/fwoYOMQ/ih0J6PgV1o8 Isu4cXQ4dh20jgdgFReFILFJ8wkKe+t3uWi4qK/vJMHtSi3vO92utzg2/PMbkSGYPA N1EzOq9Aj44UIr8INxTuHHDN1efAPeB1WW3s7M6Gcg1O6/nOjFGkBFN1DWQacC7By1 bvexOIZIsTvoqRsw4U1XrxeeQDyN59dZ51q8Yg5wsEmBvXqLLoJh70EYIt9IP83qS4 nwnA108U1fN4g== Message-ID: <8ca84535-861c-4ab0-a46b-5dfe319ac8ac@kernel.org> Date: Fri, 27 Feb 2026 09:45:07 +0100 Precedence: bulk X-Mailing-List: linux-kernel@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 , Pankaj Raghav Cc: 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> 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 06:31, Matthew Wilcox wrote: > On Sat, Dec 06, 2025 at 04:08:55AM +0100, Pankaj Raghav wrote: >> There are multiple solutions to solve this problem and this is one of >> them with minimal changes. I plan on discussing possible other solutions >> at the talk. > > Here's an argument. The one remaining caller of add_to_page_cache_lru() > is ramfs_nommu_expand_for_mapping(). Attached is a patch which > eliminates it ... but it doesn't compile because folio_split() is > undefined on nommu. I guess it would be rather trivial to just replace add_to_page_cache_lru() by filemap_add_folio() in below code. In the current code base that should work just great unless I am missing something important. > > 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. Could someone stumble over the large folio after already adding it to the pagecache, but before splitting it? I guess we'd need to hold the folio lock. 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. 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 -- Cheers, David