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[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 MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: EC82B18000C X-Stat-Signature: izr1tr4d7ynz73fk4wraxn6jburr96yk X-HE-Tag: 1783517781-385037 X-HE-Meta: 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 9gGRfiM7 UckSFpBVo+SPxlr7HJUNFjcPTTTVs8O6fu10mDVl4c2R7bdbr4YEgphpeff1krNOK8rk8BZ9twXIhzKdlmJMoyhhWujc681slZCecbCzpw1586s9yH5Ig42xHPqKA9gCaowrbWBasneDYg9zoAV40Cf2BcyDlskvN+KOCtpbzKOT3i+GsV1oc64bFYbME6rq2NwgVA5UmrVD6KMBexLgMSvuzQAWMBoVgSeoyFaZM+ZaDEp2cu+AwmVX99t8JARuSpf1mmW0f1FPuO79vITqKuSuXo0JiVzgig2IOuIHnF6eeDXXwSlUTt9n3ugjBQAuwj/akur8tfalxqVsu/ODu5vYQ1Tv1sVmdC7cKdU/B774F5EsFwm2IVBCEbCW9xDkUx6BECUh0basGB7e8rOIBxQALAA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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