From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794245056; b=3hzJ/ufreFwz04Znv73Jkz9PalesQMEEiciIszrFeFacrdsVYezBG01qVK5HGpIXSi/H trnoNolOsmSOHi3KeEvL7rORn+23Fr4vRJiA7+P/Ecbwhqf7YaVjQlS20E0Sg0v2onEk5 WPhfyVj/Ist7QOat67k7zwToElQlWPL3uB+WvKoxukt/ULEx5TuTQwGGDOxPon8Ic4XAT MP0+6iNFzvcPxiW0/pyqkJREPhEeWa/7H0LVn9DiRO1UkrJTzZoyce8e45y1l3Ul9opIP xZgyvkliD0rgwvdrKUy1cV52M4Fjn9i+ji0hgfD+opru5GMDuuvtD/kqJIpLp36bq5g== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794245056; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=/aSAxr7TF1nfjT/HWiDs+7ns10jo5fbdPg/x0SCDIHs=; b=IXwAoMCw3h3dBmiRM7KPb4jxmNjWbdeT4WNRpfS5Mn/4LMMY24xGRQ4Mzai1yHaCKgw2 vuGxNKi+u+a6UDq0nZJ+Lx4EqyHamlwkaCvQDv4O3TiceuBKKdNSm7Efj85tJAm5wLSEr 8ttY82WHQQ4teJBEWCKWILrghczEoxFV4WPxVoswg+43wE2LIeK7ZVpwHRHV8PHthgcWC EAi50/9Lpbm28lOlkMVMCK0n2fIn9mHAEqRKmn3j99fqLskJFUSsqITJmtY1SNdp4qxoz v/HhHq6ucj8h7Oip6ywyGC8hCCiU//U7hO1pJhEQrS0Vdm1tq6bDeShYe/EmsMWR0dw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=iDxqQhow; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B0C60606A321; Mon, 9 Nov 2026 17:24:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=iDxqQhow Received: by smtp.kernel.org (Postfix) with ESMTPSA id F2FD51F008A3; Mon, 9 Nov 2026 17:24:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794245055; bh=/aSAxr7TF1nfjT/HWiDs+7ns10jo5fbdPg/x0SCDIHs=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=iDxqQhowEYVH36uK8isMhxGwgKmT4ozWL9rSdUjNWzrBo3moZtLoNOSvoVSUND1DU Z8AD+H/zvOBRivvUcXJxAh4a4AZz2ZNDg55SbcCfObS90h8dUDN60lUYO71TVIOhY8 Y1GstciRTQt0rYz+zKmsbn1pPvifXUMe1fnnfIkU4WLLMhL/c/5m69u63sLKRX8XVk 1AV+QUD+WE2Xbj8s0b+cviQC7bEr3H1n0iHRSST8nMw681/5s+LA0KtcxsuqbFQW9c 6tqcoOl7W1dz0n+qVrfeJE8TA1jc4cLRLlL3cWGuak+W4c9NURwTpeu/h+DCgKeTV/ 1VzI36dbDHEEg== Message-ID: <8504e28f-faeb-41e3-842e-0cb74d1a25ad@kernel.org> Date: Mon, 9 Nov 2026 18:23:58 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v2 01/18] mm: free PG_rcu_free folios only after an RCU grace period To: Linus Torvalds Cc: Kiryl Shutsemau , Andrew Morton , Matthew Wilcox , Vlastimil Babka , Lorenzo Stoakes , Jan Kara , Hugh Dickins , Christian Brauner , Alexander Viro , Harry Yoo , Miklos Szeredi , Miaohe Lin , Naoya Horiguchi , Oscar Salvador , "Liam R. Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kairui Song , Qi Zheng , Shakeel Butt , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , "Paul E. McKenney" , Pedro Falcato , Luis Chamberlain , Ilya Gladyshev , Jaegeuk Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, fuse-devel@lists.linux.dev, kernel-team@meta.com References: <20261104130118.2507513-1-kas@kernel.org> <20261104130118.2507513-2-kas@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 11/9/26 16:56, Linus Torvalds wrote: > On Mon, 9 Nov 2026 at 06:43, David Hildenbrand (Arm) wrote: >> >> Can we just rework that code first to have some clear folio freeing path, IOW >> doing this in a folio-specific helper? > > I think you're making things worse rather than better. The current code deals with pages vs. folios in ways that already makes this code only work with folios even in the short term. We'll be starting to let page_folio() fail soon on things that are not actual folios. PG_folio for that is already in the works. > > The whole point was to hook into *one* place: the page freeing. Right, and I'd hook into the folio freeing path if it is folio-specific. And we will need clean path for freeing folios either way as we are starting to decouple struct page from struct folio as envisioned by Willy. If we actually manage to make this generic for different memdescs in the future, it can obviously stay on the generic path. > > Trying to make it specific to one special freeing path only makes it > fragile and less obvious, and results in anybody who then uses some > other freeing model to miss the RCU thing. > > It also means that suddenly nobody else can use the RCU path for their own uses. > > Look at all the kmalloc RCU freeing: it's used all over the place. RCU > has basically taken over the kernel. Every single performance-critical > lock-free area of the kernel wants RCU freeing. > > I think trying to corral it into some special case is the last thing > we want to do. It only makes things less potentially useful and more > fragile. Let me wrap my head around how this would look when we decouple pages from folios, where pages might not have a ->lru anymore, or not even a refcount. -- Cheers, David