From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E600DCA5FA2 for ; Mon, 28 Sep 2026 19:12:38 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 025286B008C; Mon, 28 Sep 2026 15:12:38 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id F3F086B0092; Mon, 28 Sep 2026 15:12:37 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E570D6B0093; Mon, 28 Sep 2026 15:12:37 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id BE3D46B008C for ; Mon, 28 Sep 2026 15:12:37 -0400 (EDT) Received: from smtpin21.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 5987BA6647 for ; Mon, 28 Sep 2026 19:12:37 +0000 (UTC) X-FDA: 85264117554.21.F6D0B8B Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf28.hostedemail.com (Postfix) with ESMTP id A2B7EC0006 for ; Mon, 28 Sep 2026 19:12:35 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=HF4S1Z78; spf=pass (imf28.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1790622755; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=3+/0gNUnAEU8rNmsasP2G1qveGjqqxqRYFGhYDQK2wU=; b=DSwmML5aAn15HOWsNgvsIK/yQuafQURSV+NIfjoI1GAKWKrMubL5OPpzWV+xHzmYECw6L6 JvGh2HDg2ZZ16JiYX6cW0hJDJAk3WKRxatkvLSQ7eNBtovL7ApD37wq0RjlcZvO3Nb5BvG zYEiUu2KBUbLi8vIyY++8AJ2wW7QON8= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1790622755; b=4E53t11a4Fh5o65ipldkQHg1Edfzvwu6FlhZo92o0LCEhmTTqqmiVrfFVPMyI8UPJ1aB3e nlPqZo2GFccE1/B23+BXXKho20WPRcIzc11npLT2UW9OYLHMw/GvxheK3LlUDL+TaLdrqu uV+Kz5TMR45TpqldWNuuUhB2ndszLbI= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=HF4S1Z78; spf=pass (imf28.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 363EB600D1; Mon, 28 Sep 2026 19:12:35 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 342441F000FF; Mon, 28 Sep 2026 19:12:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790622754; bh=3+/0gNUnAEU8rNmsasP2G1qveGjqqxqRYFGhYDQK2wU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=HF4S1Z78mScB4lUcYE6JWgmNHRRxIQxkpRj14G/OgV77GYc4NE9XRSxU/WrA7/o8T jHkuFt25YUOT+mG7iVW/hfP8bxMYMWq+WXAe+owB06S0SeE7wPQfrkwVXLE/DAcWtM ARw16ifk79EF7PM9ra6qxCAQxqKbrhfgbt8qls/bYL6rB77cjM4/+zlUULjLLBP+6h LFlEEaVZ0FA6vtFPLORpsHWqiw8cLu9tB3uLGAvnMpvEPc5eo9P2DMndfHhT7A5ikY TB/6cHvErfozrqwxtPPtJqT7/S6cCELTRktjxG3EPzSnTXaoCjxGwaMJKZBMkp8Q/E RSAYk6NBbI7bw== Message-ID: <85aff663-2131-47da-ac04-8f0799a49b91@kernel.org> Date: Mon, 28 Sep 2026 21:12:30 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC] madvise: best-effort deferred writeback for shared file mappings To: =?UTF-8?B?5aSp54u8?= Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, "Lorenzo Stoakes (Arm)" , "Liam R. Howlett" , Vlastimil Babka , Jann Horn References: <7ebe4591-2306-4b5c-b83e-6a2e34b52bd8@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: 8bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: A2B7EC0006 X-Stat-Signature: 4i8iteg5pkrj1ozgguioc5ydt94sg9ot X-Rspam-User: X-HE-Tag: 1790622755-226653 X-HE-Meta: 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 FGhu5J7G eLnViZTSXrDAUJWNdNFl+UJVK1HTkWHbyaO+0x106h8eITnQjOfeFcvPohLE/vR2O/+uqbjuj11aYszK9OqYYXa5qpv4JJSxP30tBQJ5l4VeHVvf672xM0Ww90Mulr5NfWs92K/uD9nnCuUb9j2UqoYW+jO1ZRt3GyLkzsnmzrYn7VmbklD0z+hqJw3hYTr3EMQ0EzrVzsm4VdIW3bWVPu5pWH5rBd4jRe9e1tyYu22QizapXokc/0928wTZA7iuRAuvfZX7068RvHD2bJqkaQpGDew== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/28/26 15:09, 天狼 wrote: > Hi David, Hi, > > The use case is a concurrent, lock-free, relocatable data structure that > uses offsets rather than absolute pointers. It implements copy-on-write > at the data-structure level and is designed to remain recoverable after > a process crash. We therefore build it directly in a file-backed > MAP_SHARED mapping, so its state is not lost when the constructing > process exits unexpectedly. What is supposed to happen if the process crashes when updating the MAP_SHARED region halfway through? It would be helpful if the use case + data structure would be explained in a bit more detail. > > Building it in anonymous memory and calling write() only after > construction would lose that state if the process crashed before the > write. It would also require copying the entire structure into the > file's page cache. Yes. Unless to would try to bypass the page cache of course (if possible for your use case). > > During construction, writes are scattered throughout the mapping, > dirtying pages rapidly and repeatedly redirtying pages that may already > have been written back. The goal is to reduce writeback of these > intermediate states while retaining the same page-cache pages for > subsequent readers. What exactly is the poblem with writeback here? Unnecessary I/O? Is writeback the problem or actual reclaim after writeback? (I recall that in a fuse server you can in theory delay the writeback request. So maybe you could get something going by serving your file through fuse and enlightening the fuse server about it. Just a random idea.) > > The hint would remain strictly best-effort: memory pressure and explicit > synchronization could override it. By "process crash," I mean termination > of the process while the kernel remains running; recovery after a system > crash or power loss is a separate durability concern. > > Regarding the interface, madvise was only a suggestion. A file-level > advisory interface would also work for this use case: deferring background > writeback for the entire file, rather than individual mapped ranges, is > acceptable. So fadvise would be an option. However, this "defer mode" is really odd. It sounds more like you would want to have a custom policy there, instead of hardcoding something that really not a lot might want. Hmmm -- Cheers, David