From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f176.google.com (mail-pl1-f176.google.com [209.85.214.176]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 79C4D342C93 for ; Wed, 8 Jul 2026 13:36:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.176 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783517782; cv=none; b=tiCBa5FIQMnJs3dCuZl/VLzQ3OHZ2ixNuUlAEzB3ff3LUynekzVBGS8pIIasBuH5pncVOf/3fm88SCzkM7+HpYmPS1u+rVKT2XTF3RbsEgn+sR7qe7g7b+D4x8o8Z1Alzr6pfPiPxOfwWalrcdSj9ZBWKo8bOjfyYKKuBBm4Z+w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783517782; c=relaxed/simple; bh=c5VKo+hme5qZWDXgseFbMKc9cMincvClbgPvanurlGM=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=fESUYpsuAzkzDhzWGWghIukatMy0rkn69ogF9s7amuFd//M3bz/cjuKT5cvHYABldhe2YEnCQMyZsJ3Ek8lQmiEJ1Na8C/GodLH2GZ0Dm7zL7O1NnxaUdYZvvMMTozEGSWfZ+sD3ADaqk101E32ZE5BaCcvvOU4XyPk0ISJDbms= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=VfC6RHDa; arc=none smtp.client-ip=209.85.214.176 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="VfC6RHDa" Received: by mail-pl1-f176.google.com with SMTP id d9443c01a7336-2cca0c5799eso5754605ad.0 for ; Wed, 08 Jul 2026 06:36:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1783517781; x=1784122581; darn=vger.kernel.org; h=content-type:mime-version:user-agent:references:in-reply-to:subject :cc:to:from:message-id:date:from:to:cc:subject:date:message-id :reply-to:content-type; bh=gyj4hWA1vtXNSml0ZMlyH4/ogXNrmE8njxVw7g3pFsU=; b=VfC6RHDauhT6LBAg6DgfnNU3KqedF++w7TbGMO/UjfFs8NVYeEC3xy/u7jauMyoBew sUZJNEFMYLe7uO4tCiWc6ax8QWIuh+Sb3/IS3BjuoJVqg1luYJRBLhqlhk6sYnaAZd+Z d+/RzDW2Nm5r45vJK9Xon50hhr17xpc8NVrPYtvXXfd++wphUe2akXMCVJEuicB0WyYA 5820BL53irosQtICDToom5TeoLFwVXF/4IbpEqXJ1vmlcm757uhoP8g2JSkj2tTJh6vq u55F+3kJLboRMBheiWvRwoqTbi+aN2nAepXtrNV6JFBp32Fl3cRDYCHAWkoBcpjMGNBh 5pCQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1783517781; x=1784122581; h=content-type:mime-version:user-agent:references:in-reply-to:subject :cc:to:from:message-id:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to:content-type; bh=gyj4hWA1vtXNSml0ZMlyH4/ogXNrmE8njxVw7g3pFsU=; b=VvPhscuZ1SPorvNcTIndA0h1gZ+zo4E/+JVcMBzLbCbFzxviFg6to8Y0K5eivXmE+r H/TfhvZSDqRVDfzo/QfhfAyesoMLxH/3QQRWtsqEe7oZPhoK+pDbaIb6T1t4coWi2D6X HDLDZ4sEAWoOt5KihfAKjUaKkMcg3pXP6zhMEtekzBXhDb5f7CdJdm0xz2qyhmGtTdJX 1IN6aqLtvw/HfTYFLLwfnqc/TuKUTAFWY0ulOECTFbvbtI/q2HKWmjM689vn8myei6hC jzuh+DHRkBZBBtFTK7ZhTIAEmOp5cqsvwdOQJsyzre+ig3Q/8dN8OtfzqaJuj1sfF8kL b5BQ== X-Forwarded-Encrypted: i=1; AHgh+Rp0a7vHDD2FR4JZr4wXAQmBMhVHvJzH3OiBq9RVn0kc7pQdwgm1iUNEMEmbSFOxAJoZJJFN7uOFs4Dn5aU=@vger.kernel.org X-Gm-Message-State: AOJu0YxaDQNc3Wc7ZaGe+3XW6T4WIk0vKNcdXP2//afec3ujqnQJ3Lnj KLfRMMBhZpY7bAt6iL5Pi7++Gx4nSbxgNAHkKzibQX0abAGVLblFNC91 X-Gm-Gg: AfdE7ckXXHP1vEULYgYxjJS4G2+EP+ue/6Mcu7zKpnMfnw61JnSc4l8EtwU7liS0+Yt HN6y7r/LakgpPjkslA6EdkRYZeoOzwoRG0YnY9ic4da7EEa/O9EnT1XchVTBqfymOyo7zSqhrVu K00Bn2UVTdi0O2xP6EY4nrBSjsY4A2FODbUHwkOMNLuirdDADghzVTSxeUtnGo7t+kvqmK8Zh5K cGCBImrEIxC+/clXcRixleZl4EyG0vLiiAoXZFBMSa7OTEZaKtjmZPoQhRO4ce1MfRIrB1ltIPI r9lg0PJ+0GDOiQjlBK0CYGkekDMbOzpUrSpZKBJgApIQev8nkgPjZ2NEAx5PYYsECis/fAL6gWM ffHXlPlHsqx6HBtVbJz7af0fJtGmU8sN/Z4HYDvkKWhbcDSHjlhlBnfbvfbCmk3UduGqrRr82yj 8LUm7nwes0YNypx6Ny8sXCy0oW6KQt39NlBGi/mmkhf9Hs9m8FdBaICxJbeJK6wdcMN8Aa6lmeO zFBT2w9KU09f/xNd3R7N+OL6ifpcAjRW5TgVwuMQeIZ X-Received: by 2002:a17:903:38c4:b0:2ca:cde5:29c4 with SMTP id d9443c01a7336-2ccea587847mr23958075ad.47.1783517780714; Wed, 08 Jul 2026 06:36:20 -0700 (PDT) Received: from mars.local.gmail.com (221x241x217x81.ap221.ftth.ucom.ne.jp. [221.241.217.81]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ccc9d5c804sm28186045ad.82.2026.07.08.06.36.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Jul 2026 06:36:20 -0700 (PDT) Date: Wed, 08 Jul 2026 22:36:17 +0900 Message-ID: From: Hajime Tazaki To: ljs@kernel.org Cc: geert@linux-m68k.org, akpm@linux-foundation.org, willy@infradead.org, liam@infradead.org, vbabka@kernel.org, jannh@google.com, pfalcato@suse.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, gerg@uclinux.org Subject: Re: [PATCH] mm: nommu: point to the write iterator upon split_vma In-Reply-To: References: <20260702012546.665383-1-thehajime@gmail.com> <20260705152708.582fd8d87561f600da23c0a7@linux-foundation.org> <20260705222343.5d5c78cbb54839c5efcaabf5@linux-foundation.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/27.2 Mule/6.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII Hello Lorenzo, On Wed, 08 Jul 2026 04:15:53 +0900, Lorenzo Stoakes wrote: > > as nommu started for embedded devices which are not easy to test, I > > agree that it is also not easy (in my opinion) to maintain. > > Indeed. > > > > > indeed, buildroot images for nommu targets (with qemu) are available, > > but running/testing each of commit to the kernel tree give me more > > than 1 hour to rebuild the images (including userspace build with long > > flat binary conversion, etc) (which I'm playing under github actions > > with riscv-nommu). > > I've struggled to even get the buildroot images to work in any way. Right now I > don't have a clear nommu test setup other than building nommu_virt_defconfig for > riscv. > > > > > # yes, should use ccache :) > > :)) > > > > > one of the goal which I am with nommu UML (*1) is to provide an > > environment which can be tested in a simple way; runs on x86 > > machines. An extension to UML means that you can also use KUnit > > infrastructure. > > Yeah. > > Well indeed my raising the 'please let us pull this out' was initially a push > back on that, because if we were going to pull it then that work would work > against it, but then it became clear that that dream wasn't possible. > > And that makes your work on that REALLY REALLY USEFUL :) so do cc me and ping me > on any respin and I'll try to find time to help. thanks, will cc from next spin. > > > > LTP (Linux Test Project) dropped the nommu tests 2 years ago (*2) > > (which is pity), but the reason is similar: no maintainers appeared > > when the project asked. > > Yeah and it's just the same thing overall with all of this. > > The companies who are apparently dependent on this need to _actually pay people > to do some even rudimentary testing_. > > nommu.c is co-maintained by me and Liam simply because we have done more to fix > issues with it than nearly anybody else recently. It's just a burden that we > took on. > > I'd far rather see an invested mm person take over if we do indeed have to live > with it :) > > I also wonder if we couldn't find a way to implement it in a more maintainable > way, perhaps as a 'virtual' mmu system somehow? > > I simply don't have the bandwidth for that myself, unfortunately. If you meant that 'a way to implement it in a more maintainable' is about the code structure, the current nommu.c is reasonably abstracted, which contributes a bit to reduce the maintenance burden. I thought that what missing is a resource of tests and eyes to look at those test results. I agree that the tests should be done by the people who are using the code. Moreover (and ideally), the code should be maintained by the people who're using. I think I can help at least the former part. For the latter part, I wish to help as well but I'm still a very immature developer of mm subsystem (who struggled with addressing Sashiko reviews...). > > I wish to be here to improve this situation, both mm/nommu subsystem > > and LTP, as well as any !CONFIG_MMU code in kernel tree. This patch > > is actually discovered during LTP (re-)integration with nommu kernel, > > which I'm going to propose to LTP. > > Your work is appreciated and welcome, thank you! :) > > > > > I hope this helps a bit. > > You're definitely helping here and again, much appreciated! m(_ _)m -- Hajime