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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 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 X-Stat-Signature: rregaiqjy86u41adcamg7tjaaaz3zpb7 X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: AD7FE180003 X-HE-Tag: 1790921336-363860 X-HE-Meta: U2FsdGVkX18nwS6AZAdLKS21UxScOvDpTrWhUqAfhZ7IwQADf0zPZF8PnfhJilXguTyH3zUcHc5TS9eJhB2EjKE1s5wzpT/u+c6Wl+vINASVeSv27ZlKgZ8ovhfFFG2NljxLPANAX/UN7Ng+sY9E/Zq0LfmLIc3aBVd9/dKUPhK3hqNpck6D61xw7xHl93BWX6IIx0d0r/mhrsch9cF58q4I2YQFvSBM8hYWFmvT/GTjlbpjxsjUkeL3WzFDQ/VeUBj2RCxMwcxKjafkIVbTDnd2212wJYbzPFFPvxdP1rMIlwGLpsKGXSEDMa3ojOTk5PVKCdIigsTr8tNiviQySREG4wlE8WuvaGkPtDToGSwmuw0Rm4UrHjsD8KDPGd1wlZ6ObFgS7gAci+Cie11aRSLI0dDDjwoL/6RRE/hToqf0VNlSQSM378d8ZYLXT9LOkVjW9st44OZ3aVfC4zvYofD4IroJ5mdHZ4sLA+fy0lPrpSFGUjpxOcldKhdWmz3SZcy+IZW7AQjb9o2vyGsa7qnNwr6UD7weipilYAx+mWDRrZcdlWSNiEbgQFy7XJMKfidzpdWeAU1C5JhYetfmgpDtPZQRNzfZlFqiI/tSb2ZBNmKm2k9peraLsvrNhOBVRtKig7TSkaRMWJG6QOV9lrFMBKOrLoQ4B5tceSWWhfebZmOzDHa1euSA+iwe1EBBU4pRf9dxxZOKGkEeqKayOnDx9XCl6VqWf6VVW16HlAo2OmyoJo37L25Kj5ZdZQACU6sFXo7axTdZqxDrguDd/8AKSdPVuSGFYZYQja8hypWw0stQEM5TOIRfDMlW6tEp65ODgdrzW06JE+JM+eMQBRV59bGRsoE2lldaqirrEoLUE4I0nATBwoyJesyUZoWJtSOFKW85eXqgHH4ooyj/qgll3Tl1IhBi5ZNN2CJZqNH5MFmXbV8om4/HnJkjrCTryyv1bWpReRwpWbHJFqW +r5nND37 TpIotfTtHnXVBXoNf6r8UzTln/TlQKFarKgxhGqYTybuEVGgCl4O05ri2Lgggkimxgg916NuVkPeWbx4VSbJh1GjzNQ47u+xh3FopuF8Wp2pl1viOoV41hXcgiH0fstJVaerQeYkTzUt3mFfDuuVhiwiptD2txDYb5A+76AUJ9uDoEBac13clSXl9+rsGTecZsSsD41YAma3Xo2lg8nvq26yierxpLB9ovbxoNkjCYI7KyErknNH+lkXpww9Mugne79GD Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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