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[221.241.217.81]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-394eb78f1a4sm7281618a91.17.2026.08.15.14.58.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 15 Aug 2026 14:58:04 -0700 (PDT) Date: Sun, 16 Aug 2026 06:58:01 +0900 Message-ID: From: Hajime Tazaki To: ljs@kernel.org Cc: linux-mm@kvack.org, geert@linux-m68k.org, daniel@thingy.jp, shuah@kernel.org, kees@kernel.org, luto@amacapital.net, wad@chromium.org, broonie@kernel.org, jackmanb@google.com, liuhangbin@gmail.com, rbm@suse.com, linux-kselftest@vger.kernel.org, linux-um@lists.infradead.org Subject: Re: [RFC PATCH 5/6] selftests: run tests on nommu architecture In-Reply-To: References: <20260813063401.1786548-1-thehajime@gmail.com> <20260813063401.1786548-6-thehajime@gmail.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/27.2 Mule/6.0 Precedence: bulk X-Mailing-List: linux-kselftest@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 On Fri, 14 Aug 2026 21:50:50 +0900, Lorenzo Stoakes (ARM) wrote: > > Not really loving this as mentioned on the cover letter. > > I'm sympathetic to making things work if it's not invasive, but now you've > essentially asking new test authors be aware of this to some degree. It is not intentional that new test authors should have to think about NOMMU=1. If there are no option specified it should be as what the current kselftest is and it it's not, it's a design failure of mine. > And making the harness - which is the defacto way of writing tests - now > simply not work there is a bit crazy. > > I'd ideally like to see _all_ tests use the harness. I also think so but if NOMMU tests is implemented using the harness test, this patchset would be invasive. This one is very small patch which tries to: - add ability to run tests on nommu - with minimum modifications and not breaking any existing usage of kselftest which are, I guess, what you're suggesting. > Also a bunch of the tests already do forking as part of the testing: > > $ cd tools/testing/selftests/mm > $ rg -l "fork\(" | wc -l > 17 > > So at this point you're not really running much of the selftests at all, > and are only happening to run those that don't do the very basic stuff > nommu can't deal with. the current situation is exactly what you described. `TARGETS=mm` is able to only build with NOMMU=1, but onlyis runnable with nommu_*_test (I need to specify `-t nommu_mmap_test -t nommu_mremap_test` to pass tests from a run. Now I'm thinking to create a different target (e.g., `TARGETS=mm/nommu`) to make it more clear for this situation. Existing tests even in selftests/mm should not involve these new tests which has such limitation. > I think an audit of existing tests to figure out what works with nommu vs > what doesn't is really unreasonable again, given nobody tests or seemingly > uses these arches. > > So this patch might beget more nommu carve outs and exceptions and > therefore nommu workload and maintenance, which isn't really sustainable. I can understand but without tests we cannot easily detect regressions in future. Like when you applied broad changes into mm and try to apply also to nommu.c, I believe these tests are also useful to verify the extension, especially if the changes are not trivial. # sorry, this might be too obvious for you.. > I know I complain about lack of testing on nommu, but at the same time I > don't think running arbitrary tests that happen to work on it and who knows > if they are valid asserts anyway really fixes things. agree. I think (current) nommu isn't ready to run arbitrary tests of mm. > And given nobody really is doing testing, it's not really a great RoI > here... At least myself, for the moment, has an interest. > ...OTOH I suppose it's a minimal change we can largely ignore as long as > this doesn't lead to additional work/auditing from anybody but nommu > enthusiasts. > > But I'm just not sure that will be the case :( again, this (not breaking existing model) is my intention so, this should be the case, and if it's not it should be addressed in this series. > (I'm amazed we support a mode in linux that can't fork() in 2026 :) I concur. > > --- > > Documentation/dev-tools/kselftest.rst | 12 ++++++++++++ > > tools/testing/selftests/kselftest/runner.sh | 9 +++++++-- > > tools/testing/selftests/kselftest_harness.h | 4 ++++ > > tools/testing/selftests/lib.mk | 8 ++++++++ > > 4 files changed, 31 insertions(+), 2 deletions(-) > > > > diff --git a/Documentation/dev-tools/kselftest.rst b/Documentation/dev-tools/kselftest.rst > > index 64c0ec7428a2..800b2b688aff 100644 > > --- a/Documentation/dev-tools/kselftest.rst > > +++ b/Documentation/dev-tools/kselftest.rst > > @@ -230,6 +230,18 @@ section:: > > > > .. _tar's auto-compress: https://www.gnu.org/software/tar/manual/html_node/gzip.html#auto_002dcompress > > > > +Build and test on nommu target > > +============================== > > + > > +If you (cross-)build kselftests for nommu targets, or run tests on nommu targets, use -- Hajime