From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 07FE638D3EE; Fri, 2 Oct 2026 21:44:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790977473; cv=none; b=hopvbfAqcuHipWWUip+75f0ti+bGsHLXcSbOVdDU5SnaoucHutXuMHHOkMq7nAStXDjMGgLhKUUHF156U84cqoPRWsr5HF+eRv7dH897eqhta/1jxTVG6l4Z++/qwzQPf8nJjc44YQdW3tz8S/7zpSlGHbLAN+9TMsXIIluK/nE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790977473; c=relaxed/simple; bh=WjY9uuASAWcKW+A9BcEvlS/UD6uyh5fsFHFWq4cQqN4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=DHRc51HUOy3rKlvq+O+F2y/1TmKk6+7yGJkDBJNEEIuZ9famyEYIkIJzbQUem2H934F+poZX4TGgJAumBHIoe+wIFGZxZ/eskKOo05WVjikIyJWNzDxHCn2fJg4XOtdB2IeDar+yPdlUEW6MKdJYEOZULuPGD/BGwvMmx/1kenI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AE3K2Vl6; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="AE3K2Vl6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 796E11F000FF; Fri, 2 Oct 2026 21:43:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790977471; bh=OA3SWpmyamGsgLm56ptL6ZZTSR6Zq7plBZES8synHmE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=AE3K2Vl6OU3amVn9J34OyDXo5u1hI3Mgm76Co3njixBfbVl64pXy3KEbB1jH8gRje QzEjOx/ZmPa7dt1h1ln0FZNOs9B5d7jj1GcFevU7BKECR4TXLrzS9x+6/afNqFrGT7 yNEKJavEShFhBifEUwBHpczx9wfA7LjwqY6fcQZfjIOxWvWmDdWdPhs8aj0q2SlDQn FYkHpHYM2SXBmscPVtj/tf8Xdi53y05kFVkFgW6wFqz/77U6tWGH7KCPpGkArViUfj tNE9xVruf47GFQGiBY8JlBhcz1AvwBdFtJMDo+bZCZePjO602Qjz/uH3K5WiBZ4yUf +Tq6ReP7g1HxA== Message-ID: Date: Fri, 2 Oct 2026 23:43:53 +0200 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: [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. 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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> <2e5a4e6c-8f9c-4050-8998-454b83f4823b@kernel.org> <3387642b-c39f-4f19-ba0c-267bbd2fe91d@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/2/26 15:59, Lorenzo Stoakes (ARM) wrote: > On Fri, Oct 02, 2026 at 03:11:27PM +0200, David Hildenbrand (Arm) wrote: >> I'd be very happy if we could find a clear way to describe "this is what we call >> user memory: anon+pagecache", if that could come handy in such a context. > > Rather than arguing about it, how about shifting things to 'what backs the > mapping' and something like: > > /* big long kdoc... */ > static inline bool vma_flags_is_mm_backed(const vma_flags_t *flags) > { > /* hugetlb is a fixed mapping, but the mm owns it entirely. */ > if (vma_flags_is_hugetlb(flags)) > return true; > > /* > * Kernel-owned mappings are populated by their owner, and fixed mappings > * have a layout the mm cannot assume ordinary fault semantics over. > */ > if (vma_flags_is_kernel_owned(flags) || > vma_flags_is_fixed_mapping(flags)) > return false; > > /* The mm has promised it may discard droppable memory at any time. */ > return !vma_flags_test_single_mask(flags, VMA_DROPPABLE); > } In my other mail I was wondering whether we could use vma_is_mm_managed() to express !vma_is_kernel_owned(). Maybe vma_is_mm_backed() could fit into that picture. Reading above I am still confused why something that expresses "backed" talks about "fixed mappings and ownership", sorry :( It's late here, and this is a hard nut to crack. What we have here is: 1) Is this an ordinary MM-managed VMA. So far so good, I understand that. (with a twist what I just learned about things that map random allocated pages through -> fault, but so far so good) 2) Is this MM "fixed" that makes expand/merge tricky, except if it's hugetlb where we can still handle it. I think VM_DONTEXPAND is also rather misnamed :( I assume it really means, using sel_mmap_policy_ops() as an example: the MM manages the things that are getting mapped in here (->fault), but the pages are not really pagecache/anon, but some other shit. So we cannot expand the mapping. Gah, so complicated. 3) Can the MM drop the pages at any time. I still think that 3) does not quite fit into that picture. Using something like "vma_is_mm_backed" to say "this is mm-managed, but all things in there come from core-mm and not some other random shit people punch into ->fault" would work for me. (not sure if there is still some other way how someone could get random pages into a VMA ... or how to catch someone not setting the DONTEXPAND flag) God, this is all such a confusing mess with so many ways of getting stuff messed up by other parts of the system. Thanks for working on cleaning that up. -- Cheers, David