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 ACC0437269A; Fri, 2 Oct 2026 06:08:56 +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=1790921339; cv=none; b=avpKrVWWZE/nmP9aqHqfgqlzSmPJcSL23At4uBl4XpuZlW4h51ocyr7iz7f9wrW/E4JH2I0d7HWN+4PsmKKUo0FYwVE9p/oQY2yQT1igRUBF+J8oKEjmEs1Pc8O0fa1NgpQHcaFqmJu/VO1FbWfsLRaMaQdAIOLFsBl/eSsJSBg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790921339; c=relaxed/simple; bh=S9WpXt8ZwaIop/LKQtEbEzXpn3nwMilU/SPTJAshtzE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=YO2m6TkLf/D9VlqTN7wJIQtQd1RbRlvOm07GwR/hRMEfVh78grHgumm59hu8gYCDT/k+lwSBGjWAFPLnUujp0L3A/2dKdQpr4C6VMHD+BAi7FXfoYFloWACbJS1t0RAYSz1QI7pd3x3TDCkRbP9TSw2qPdpCfe1ot9EMtVqSdvg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=k0n9BCZe; 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="k0n9BCZe" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E2A121F000FF; Fri, 2 Oct 2026 06:08:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790921335; bh=agu/VYOjK7kNVTsVW73qyg7EU19zxMLH1H7KJB1gnL4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=k0n9BCZe437AIaCN19WoBh6UpkVlB2OxIuvSMocblVpda5vLUmTgjqGfsI2ij+gc9 p+tACWkGa+lgasOyQy9dpA5rbxE+OcN8wJrMmPyYIkS3O37Yhy3rb/w+HGeOVJM/ft GVV7seGQ6yEQrb+r51pcfaI9C8bc/TAJuL3eNo12qZzYKc+B7nW3p+BieXJcWK3hZu +JCjVCQJPTpKp55e6dCyPb0Lbcg0/hp0hB3+CuNLPMFUZl+/KZxrNUJRGDUWc26FIk 66aOBLsMXaUrnXxfL14PiUHqIEkBT95W/7polM1nzak6lzT0iCGcHpX5nGMJxg6HWq vcK3+mBQ/Z1WQ== Message-ID: Date: Fri, 2 Oct 2026 08:08:44 +0200 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/2] selftests: run tests on nommu architecture To: Hajime Tazaki , johannes@sipsolutions.net Cc: ljs@kernel.org, linux-mm@kvack.org, liam@infradead.org, rbm@suse.com, akpm@linux-foundation.org, luto@amacapital.net, brendan.jackman@linux.dev, liuhangbin@gmail.com, corbet@lwn.net, kees@kernel.org, broonie@kernel.org, mhocko@suse.com, rppt@kernel.org, shuah@kernel.org, surenb@google.com, vbabka@kernel.org, wad@chromium.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-um@lists.infradead.org, geert@linux-m68k.org, daniel@thingy.jp References: <20260929235711.2287931-1-thehajime@gmail.com> <20260929235711.2287931-2-thehajime@gmail.com> <94759bed23f00d2044005e36be6f72f297e092f0.camel@sipsolutions.net> 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 04:38, Hajime Tazaki wrote: > > David, Lorenzo, Johannes, > > thanks for the comments and inputs. > > On Thu, 01 Oct 2026 19:01:45 +0900, > Johannes Berg wrote: >>> >>> I thought maybe uname could help but our LLM overlords tell me no. >> >> Hajime originally wanted uname to indicate it, but that caused >> regressions elsewhere, so we dropped that commit. I guess we could put >> _something_ back? > > systemd uses uname information and our (old) patch changing the format > triggered the regression. thus, we dropped it. > >>> It pointed at something though. >>> >>> In fs/proc/meminfo.c: >>> >>> #ifndef CONFIG_MMU >>> show_val_kb(m, "MmapCopy: ", >>> (unsigned long)atomic_long_read(&mmap_pages_allocated)); >>> #endif >>> >>> So MmapCopy in /proc/meminfo tells us definitively, weirdly enough. >> >> Hyrum's law and all that, but I guess it's not highly likely to (want >> to) change :) > > a runtime detection is nice. > > scanning /proc/meminfo might be useful. although it requires to mount > procfs (we can actually skip procfs mount as it is optional) so, this > is not 100% portable. > > checking ENOSYS like syscall(SYS_mprotect) might be useful but I > wasn't sure if this is always the case of NOMMU or not. > I assume there are plenty of other mechanisms. Like testing if fork isn't allowed. > My original attempt was to use include/generated/autoconf.h; with that > we can omit environmental variable or command argument of NOMMU=1, > but gave up with handling standalone build/test case which might miss > the generated file (and complicate the patch only for the NOMMU > detection). > > So, specifying NOMMU=1 is my previous, though dirty, conclusion. Let's avoid making it harder on users by doing some runtime detection. -- Cheers, David