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 653DFCA5FE2 for ; Fri, 2 Oct 2026 12:35:47 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 666436B0088; Fri, 2 Oct 2026 08:35:46 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 617826B008A; Fri, 2 Oct 2026 08:35:46 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4DE6A6B008C; Fri, 2 Oct 2026 08:35:46 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 245716B0088 for ; Fri, 2 Oct 2026 08:35:46 -0400 (EDT) Received: from smtpin15.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id A4A8D1A06FA for ; Fri, 2 Oct 2026 12:35:45 +0000 (UTC) X-FDA: 85277632650.15.AB80D15 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf24.hostedemail.com (Postfix) with ESMTP id F28BF180002 for ; Fri, 2 Oct 2026 12:35:43 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=EYCZV7o7; spf=pass (imf24.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=1790944544; 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=0iXaN+HnW5WJtOFxnblbT6Y5Ug6Tdqox+cZXIs6Fkmc=; b=DDkdn4U1rkt0B5JTcxNQIp8NQflb3fRtrYqWOhEnVFqFjIJZd9V8sbwckH1bRPovJndpmV 0vNPUgu+Otgtt1nq/YCVIsx18hBXrRPjSqSmra6SDmh0Q1MYnBdrYY1+WAtYa9P1gZMX48 TJtuayBqnY2iZ8tQuTwKk6luhI175TI= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=EYCZV7o7; spf=pass (imf24.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-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1790944544; b=baHuKh8bcZZfFCjsqYbWYkKz7mzafcHMETKGTaoMDii3+m9B1bhjWTh+V4CRjFU9TNOIWT 3Kp1YiPVQh4gmdS6j9QdYSfchUq4yNQ1PxlsKdjV4Qpd3gKUpjB+mcXenJoMbpM4ESzUKb G3+1M0Yzl9AUcgT/eRcgkC4EYSc+e20= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id E436E60A8C; Fri, 2 Oct 2026 12:35:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 365B11F000FF; Fri, 2 Oct 2026 12:35:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790944542; bh=0iXaN+HnW5WJtOFxnblbT6Y5Ug6Tdqox+cZXIs6Fkmc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=EYCZV7o7nZ2EHWJbbgb0R5iyQyoRPWyVamUzrLEUgn3UGMmRcgPRwbvtm3FqlL9nI PtAu9WC3TuipWyvSLOVKQ9Z2b9ifc0Rmrh4+E8tzP7JgzlYyRvMEPMH44dPbGaJ0Cu YG7DYoV6uJzj9ziEGsAlpUgkrkbIQvetREa7FIUF6+l4jqbtu5pSxjKp5eEV1p5QuS 4QjOYcLE9QneXF8hOQO4twzQ5zBbruCfgbXA+Gzce8OGNcDtErFNr95a4oqqVg10nc pwEwxBhKGhJ/7WgtKtlJKBg6ltkndikRhcXkn9tzHXMlafKoUkM7mCyP2COLF9XQWK PoE9yFxy7Ring== Message-ID: <2e5a4e6c-8f9c-4050-8998-454b83f4823b@kernel.org> Date: Fri, 2 Oct 2026 14:35:06 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 31/40] mm/vma: introduce vma[_flags]_is_persistent() To: "Lorenzo Stoakes (ARM)" Cc: Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Jann Horn , Pedro Falcato , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jonathan Corbet , Greg Kroah-Hartman , Dennis Dalessandro , Jason Gunthorpe , Leon Romanovsky , Paul Moore , Stephen Smalley , Jaroslav Kysela , Takashi Iwai , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Doug Gilbert , "James E.J. Bottomley" , "Martin K. Petersen" , Jaya Kumar , Simona Vetter , Helge Deller , Sebastian Reichel , John Hubbard , Peter Xu , Masami Hiramatsu , Oleg Nesterov , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Rik van Riel , Harry Yoo , Juri Lelli , Vincent Guittot , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Arnd Bergmann , Muchun Song , Oscar Salvador , "Matthew Wilcox (Oracle)" , Jan Kara , Marc Zyngier , Oliver Upton , Catalin Marinas , Madhavan Srinivasan , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , "David S. Miller" , Andreas Larsson , Alexander Viro , Christian Brauner , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Youngjun Park , Johannes Weiner , Qi Zheng , Shakeel Butt , Axel Rasmussen , Yuanchu Xie , Wei Xu , Chengming Zhou , Michal Hocko , Miklos Szeredi , Xu Xin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-usb@vger.kernel.org, linux-rdma@vger.kernel.org, selinux@vger.kernel.org, linux-sound@vger.kernel.org, bpf@vger.kernel.org, linux-scsi@vger.kernel.org, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, fuse-devel@lists.linux.dev References: <20260917-b4-mmap-prepare-vma-flag-sanify-v3-0-4583d8a23bca@kernel.org> <20260917-b4-mmap-prepare-vma-flag-sanify-v3-31-4583d8a23bca@kernel.org> <9bbdf4e8-6984-4477-a183-f0b236047381@kernel.org> <3557015d-23dd-41ef-9832-78b58587f3f4@kernel.org> <81e1e5ae-0aab-4584-81e6-3fc9c2634d07@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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How many more users will we have for >>> that function? > > Anything that requires stuff not to be dropped behind the user's back, which is > at least 4 cases! > > That being open-coded all over the place is a problem I think, and I think stuff > like the PMD device private are a reminder that open-coding all over can cause > problems. > >>> >>> If it's "no others" then please don't add a helper function with misleading >>> names for it and just keep the special "dumpable" check in the new form in >>> madvise_vma_behavior(). >> >> Talking to myself ... the more usage I see of the vma_is_persistent() the more I >> think this shouldn't be a helper at all. Especially not one with such a >> confusing name :P > > There are 4 open-coded checks that test four ad-hoc flag combinations checking > for the same thing - 'can the kernel or a driver change things or discard stuff > behind my back?' > > So abstracting that to a helper, alongside the other 'let's ask based on > semantics' helpers, seems sensible. > > Maybe invert the meaning to make it clearer? > > vma_kernel_may_change_contents()? > This is all super confusing and I don't think we should try to describe the semantics that way. Just imagine having udmabuf use a PFNMAP of folios obtained from shmem. For sure the kernel could now change the shmem pages that are mapped in some ordinary VMA. Likely we don't have to squeeze everything into a single helper that is hard to describe. Maybe we can pull parts of it into a separate helper with semantics that are easier to describe? vma_is_user_memory() && !vma_is_droppable_memory() Although I am not sure user_memory is exactly precise (pagecache+anon) and what we want? It's all super confusing (thanks for deciphering it). > vma_contents_may_change() is shorter but easily confused with something being > writable by userland etc. > > Or maybe: > > vma_is_volatile() > > ? > > Which is analogous to the meaning of the volatile keyword. This is all confusing because persistent and volatile are established concept when talking about memory. And see my example above, it's not even clear what it means that "the kernel can modify something". -- Cheers, David