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[221.241.217.81]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-84e175ce455sm1893874b3a.48.2026.07.22.14.17.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Jul 2026 14:17:01 -0700 (PDT) Date: Thu, 23 Jul 2026 06:16:59 +0900 Message-ID: From: Hajime Tazaki To: johannes@sipsolutions.net Cc: linux-um@lists.infradead.org, ljs@kernel.org, liam@infradead.org Subject: Re: [RFC PATCH 0/9] simplified UML/NOMMU approach In-Reply-To: <860318a2d3434c35c3bf188776093cb46f2fe152.camel@sipsolutions.net> References: <20260720185103.530603-11-johannes@sipsolutions.net> <860318a2d3434c35c3bf188776093cb46f2fe152.camel@sipsolutions.net> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/27.2 Mule/6.0 CBC: thehajime@gmail.com MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260722_141703_255486_D873F09B X-CRM114-Status: GOOD ( 29.60 ) X-BeenThere: linux-um@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-um" Errors-To: linux-um-bounces+linux-um=archiver.kernel.org@lists.infradead.org Hello, # +Cc: Lorenzo, Liam, On Wed, 22 Jul 2026 16:46:31 +0900, Johannes Berg wrote: > > um-nommu(seccomp) 3533 > > um-nommu-skas 27844 > > um-nommu-skas(seccomp) 26387 > > I'm a bit surprised these have such a huge difference, do you see any > obvious explanation for that? > > But I'm also still not really convinced that it matters at all. I have explained this in the message below: https://lore.kernel.org/all/m2y0nqwbzg.wl-thehajime@gmail.com/ # was also covered in my netdevconf talk but in a backup slide. https://speakerdeck.com/thehajime/nommu-uml-netdev-0x1a?slide=28 > > What is your plan for this RFC ? > > Well, first I wanted to hear what you think :-) :) > > I'm pretty fine with this (skas nommu) mode for nommu UML; it > > is certainly useful to detect more bugs if it is available in UML. > > Yeah, that was mostly my intent - to show a path forward for the nommu > (kunit) testing in UML, without all the other complexity. understand. > > I would also like to ask maintainers if my nommu approach can be an > > opt-in feature only when specific kernel config is added, probably > > marking as '(EXPERIMENTAL)' or `if EXPERT` condition, as there is > > potential benefits (speed, less host process use, etc.). > > > > But if you (maintainers) wish and feel this as not an easy option, > > I can work for it with later patches as an extension. > > Personally, I've always mostly thought that there isn't really a good > use case (or perhaps that you haven't really convinced me of one) that > actually requires the speed benefit, but I guess I can't really decide > that by myself. :) understand too. actually one of my motivation to give a talk at netdevconf was to present a use-case of the speed benefit. but I'd like to rephrase this motivation in a different thread; I wish to move forward nommu UML as mm folks (cc-ed) might think it's useful. > > btw, maybe I need a better name for (my) nommu code using different > > syscall handling, with regard to skas (i.e., separate kernel address > > space) mode (e.g., CONFIG_UML_NOMMU_SAS (single address space) etc.). > > Oh, I didn't even remember now that "skas" was meant to mean "separate > kernel address space". To me this is all a quirk of history ... we > probably shouldn't read too much into it now. Personally, I think skas still does make sense from the host address space pov; uml kernel and uml-userspace processes are in different address space. that's what I meant in CONFIG_UML_NOMMU_SAS in my previous email. -- Hajime