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Thu, 01 Oct 2026 19:38:59 -0700 (PDT) Received: from mars.local.gmail.com ([240a:61:8063:c5f3:3cbb:dbfe:34ef:b37e]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3a4f46bc991sm6682074a91.4.2026.10.01.19.38.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Oct 2026 19:38:58 -0700 (PDT) Date: Fri, 02 Oct 2026 11:38:51 +0900 Message-ID: From: Hajime Tazaki To: johannes@sipsolutions.net Cc: ljs@kernel.org, david@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 Subject: Re: [PATCH v4 1/2] selftests: run tests on nommu architecture In-Reply-To: <94759bed23f00d2044005e36be6f72f297e092f0.camel@sipsolutions.net> References: <20260929235711.2287931-1-thehajime@gmail.com> <20260929235711.2287931-2-thehajime@gmail.com> <94759bed23f00d2044005e36be6f72f297e092f0.camel@sipsolutions.net> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/27.2 Mule/6.0 MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: A49D81C0004 X-Rspam-User: X-Stat-Signature: 31aj9c3r9ep8ixrgzt975ukszyhneop7 X-HE-Tag: 1790908740-527297 X-HE-Meta: U2FsdGVkX1+8XrrGpm97c9xbbQQVSN6t0oaQiD6HZFXjxOD20ZAShEq9hx5qaIFVAkyEDK/FUqnB0roYk8HMpCbXkdOiHcQX/JL4TvRHV7mXWswrNVPX9lYTGd3dxY/dTlga6kMK9YmBnfl1WXyBZ2lF6VwvYMYJRDLkhkRHOZgk6zhgLbeZi63qz0GvleIxcilM8nLDFP5pY5gRHWeWC+s7hhnk1J/Ldu56FCIS3f0E4ItxBfqPACU65qtOWawk9adgiUraKXCzEC1fGvLQ3A9ET7wqdcMu5PWKkGpfGwuL4lNObR53KS8+mrzF6f47wBpaeooyAQ6FT78KI7tnR58Ho+pTUoiWY76pLmrYn4HRchZUq9jvvQH42K0p+lSoIAiBjIp/v1VRlyBq1p61n9UFFMcPDUosm1kka4ogHBBisdIq/PkidEpavx6ed0HKy7+Mpw4sPY6hOCJ+94RU9HaF8lGb2JWYCFXbyZpp0FRsx7qiFKwHWnMoXcZThNkvVL6SGYbwJKVaxrBvm1Xl+QyTEwaxORR5gDM24L4/S1NPqEbL2KKB8ELQ625LYfO9S/PnW/t2FocOLgTyd3LHYv/lCwhKqRFbFyrCQF8BT/NnKtIxpN2YculTeqwjX4AT2S1PZ+/4AxqJqjk54o/TWyQeco1vTeFCgsrzXXWt5ic9gD9IXA1USq0lXknQV9tsQNqZJ1GayD9lUneUeQUeqYkgLNIGMIpv2guNu4zFER+kGYtMB7/a/niDibj8JYveD9ZD1hywEkPH3tYEXApUlzGPY5WvsyMNq34wDa2FcW8HJWwLhHsgLEegqmIHfQPfUM1hybAx0LW6Z7gPzf2ifSUDc1qrcVLy1NleA1aFJRbKHGvcou0Ev5iVVZtlAop3T+7aAAZvUod561WgUqrurkDEmLHaj/YlPStzwyjQ43jZs7ZmMa28YrPlpKlWV7iXq9NOmfrG6oA1AFsUaPx kdk30Hbc QIHsO5C8NJBTfOmC/ja1fyTQef2YdVl8d9BEjMzSoPJVCXoPSiurnbsWTPEkk4mt35asH9YIq9ouJwyTg1A9aErqzlxpAkS5iEq3TxPKro50AYjM7/IgB69aWM0MNoRrsCC4NuCeflNyCvwCwjwqvV+TAUy9KawIjVsIqZwmyBOPue8XyASAmXBozCiB4DdZy9ha/G9hPbuZ+6v7pGmJY+Qdfx7G25qC23BWQDJHp5BnLLvJyZrvuhPqAAhTSYcbnyDVCmuzasiLzvQ8JXp66lyi4UlbWjHUGi6az8hxUt3gxxwd7/xeYYSwgCQ9amCbnGP+T5zWZC8jhPfa1wVPjSJ+Qk6u68n6ET6akSs/JsiAIWuQlEYRZ/M4KcV4WsQxTh/qMKtB3/uZrBkU5tOHkG0k9DeRF1GmpBdXpG4Ajv8Lp9z56WhXUI9Rybo1XJRgi9AaW Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: David, Lorenzo, Johannes, thanks for the comments and inputs. On Thu, 01 Oct 2026 19:01:45 +0900, Johannes Berg wrote: > > > $ make ARCH=um NOMMU=1 O=build kselftest-all TARGETS=nommu > > > > $ make ARCH=um NOMMU=1 O=build kselftest-install TARGETS=nommu > > > > $ NOMMU=1 ./build/kselftest/kselftest_install/run_kselftest.sh -p \ > > > > -c nommu > > > > > > Is there a way we could derive that from the environment in one of these cases? > > > > 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. 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. -- Hajime