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[221.241.217.81]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-394eb7539d3sm2774290a91.15.2026.08.14.05.42.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 14 Aug 2026 05:43:00 -0700 (PDT) Date: Fri, 14 Aug 2026 21:42:57 +0900 Message-ID: From: Hajime Tazaki To: ljs@kernel.org Cc: daniel@thingy.jp, gregkh@linuxfoundation.org, linux-mm@kvack.org, geert@linux-m68k.org, arnd@arndb.de, willy@infradead.org, jack@suse.cz, akpm@linux-foundation.org, liam@infradead.org, vbabka@kernel.org, jannh@google.com, pfalcato@suse.de, linux-fsdevel@vger.kernel.org Subject: Re: [RFC PATCH 3/6] mm: nommu: fix an issue on map request to /dev/zero In-Reply-To: References: <20260813063401.1786548-1-thehajime@gmail.com> <20260813063401.1786548-4-thehajime@gmail.com> <2026081355-remold-sterility-84f9@gregkh> 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-Queue-Id: 5A67518000B X-Rspamd-Server: rspam10 X-Rspam-User: X-Stat-Signature: wouss5brqfqpfknq77hukfdozkfat6mp X-HE-Tag: 1786711382-114309 X-HE-Meta: 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 kFiDzrwu 1JUenvC8sD+RdYYybBq2oG1UpswLcGzKQzAiePyP93pVxNllrnf2Lja4E3DIYg+Xv6GG1T8MgjNMmbqrOcZeAkBsa6cadZl86u1MJVolX8Lfegzi5iJMmjAfjWYQZCY7BXao96IiHTr3NFgmUjrtpD7mCsDA4j78mN6Jq5L31Zg2rjQ/d3mzwFK4P5ftp4VuslElnjBflWrdPCDZl9bjawnenoRht0c1neIEcqm4SjiaAuDPL29ydkMjoOSflm76/iQS6OCWwxIy+lgzTom5TKSghCahQKvVvopwVXaoCtc+q9BZ55mYvY0od8i1+9O75GhbciogC5SiR0FX4fuLW5ulPBzrrnrCKPq90hs6I4Z95roTTkn/AyWHWQ7A9ZCoTvA3TgU22vVnWbAp+YIY5jAu2nP3T57fRs14tMO9CfR/l0bc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hello Lorenzo, On Thu, 13 Aug 2026 22:29:38 +0900, Lorenzo Stoakes (ARM) wrote: > > On Thu, Aug 13, 2026 at 09:43:37PM +0900, Daniel Palmer wrote: > > Hi Greg, > > > > On Thu, 13 Aug 2026 at 21:26, Greg Kroah-Hartman > > wrote: > > > > > Given the age of this issue, I don't think anyone uses no-mmu systems > > > anymore :( > > > > There are a few of us using it for hobby stuff[0][1] and there are > > apparently people using it for actual commercial stuff. > > There was a session about this at LPC 2025... > > > > One of the big problems for nommu seems to be that everyone is > > convinced it is completely unused and totally broken. :) > > No, the issue is that nobody seems to do any testing or contribute any code > aside from at least Hajime (thanks Haijme :), and possibly others (forgive me if > I am missing people's names here!) > > There's been situtions where nommu has been broken for a year and _nobody > noticed_. > > And yet whenever nommu comes up people always seem to pop up and say how > important it is, then mention a talk etc. > > Well if it's important, test it. Test the tip kernel. Report bugs. Contribute > code. Any or all of it :) > > Meanwhile we in mm have to _constantly_ fix stuff up in nommu because it's a > total mess and has real maintenance overhead. > > Having to account for legacy systems that make no sense in 2026 when you're > trying to make improvements to systems people use, or not being able to do > certain things, really grates after a while. > > I mean if you don't believe me git log mm/nommu.c. This overhead reason is why I > now co-maintain it. after spending more times to look at code, fixing issues, finding other flaws, etc, now I become to understand what you meant in past emails, when you're saying a more maintainable way of implementation of nommu.c. Since I wish to use nommu.c in future with the latest kernel, I'd like to contribute it for, let's say, refactoring the nommu component which mm subsystem currently has. but for the moment, I wish to start with introducing test cases from very basic checks (which is in the [6/6] patch of this series). Without such a base, we may not have any chances to improve this nasty situation of nommu component in mm subsystem. # this motivation also applies to LTP (linux test project) which currently doesn't support running tests on nommu platforms (I've already started). And also as I mentioned before, ideally the code should be maintained by people who use it. And if I claimed that I used/use/will use nommu.c, I wish to maintain this, or at least wish to help to decrease the overhead of maintainers. This series is a very fist step toward this. I hope it clarifies a bit for your concerns, -- Hajime