From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 308FAC43602 for ; Mon, 6 Jul 2026 12:58:00 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 1C8EA6B00A1; Mon, 6 Jul 2026 08:57:59 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1A0F26B00B9; Mon, 6 Jul 2026 08:57:59 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 092076B00BB; Mon, 6 Jul 2026 08:57:59 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id CCF686B00A1 for ; Mon, 6 Jul 2026 08:57:58 -0400 (EDT) Received: from smtpin23.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 4B8DE8DC79 for ; Mon, 6 Jul 2026 12:57:58 +0000 (UTC) X-FDA: 84958354236.23.37BD3C1 Received: from mail-pf1-f177.google.com (mail-pf1-f177.google.com [209.85.210.177]) by imf07.hostedemail.com (Postfix) with ESMTP id 74FC74000B for ; Mon, 6 Jul 2026 12:57:56 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=gmail.com header.s=20251104 header.b=GryvCmtv; spf=pass (imf07.hostedemail.com: domain of thehajime@gmail.com designates 209.85.210.177 as permitted sender) smtp.mailfrom=thehajime@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1783342676; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=hO5ho4KeiiLfcBaCI+3UMPtuUVrSULK4qaWn/9TzQms=; b=Azb5fQqFSrST3wdNZsZDeudPZxV2OPFT3sSO9RWs8ysZQQ06SPpGd//H+SI3hNgXekVaVz d4q2fIZ7iRzTEmulaHyzENYQdUaMxtz7MnYyrSSEch8BsHJQCSJQPp33Fr7URTM/5r3Aqu D3jzdLU0F4QUx2FcXGkqlb8SxGnZklU= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=gmail.com header.s=20251104 header.b=GryvCmtv; spf=pass (imf07.hostedemail.com: domain of thehajime@gmail.com designates 209.85.210.177 as permitted sender) smtp.mailfrom=thehajime@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1783342676; b=5aAo9K+ip4REuvVlpMRh7reO/UCjfzasF8dIo4N2NZ7m6w8eT6Jqa2+9ALWzZsUt/bFovp nTXClyto2kF67S8FqhVYPMcCUfEqQ74mS1XU5/74VY7WT2MbF/Du4p7nEs01JVsHWLuh+X ZSiaBWtXet8IZw2LjzWyXIDuQFb3TC4= Received: by mail-pf1-f177.google.com with SMTP id d2e1a72fcca58-847917c3678so2186426b3a.1 for ; Mon, 06 Jul 2026 05:57:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1783342675; x=1783947475; darn=kvack.org; h=content-transfer-encoding:mime-version:user-agent:references :in-reply-to:subject:cc:to:from:message-id:date:from:to:cc:subject :date:message-id:reply-to; bh=hO5ho4KeiiLfcBaCI+3UMPtuUVrSULK4qaWn/9TzQms=; b=GryvCmtvJvaq6zNHdPXpkLuXU3eao9Wp0ZnT+d7kCu4c8HybTpjISO30MKevDEZ5Be pzCCsDkURaXB7MXgSi976Cz0szEaUEGUE9rVTMkZc2rGcizh2WWwmXANdJEIAU9f8J+j NzDDw03MGNl2G0d2HGefasmB2AZ28SaNXJ6kZFUxb9YiCMDIl228wak9yK2NU41dCQ8N p3h6MJ8uIdFHVTik2hXDsmS/+UUfAfCpyTmM15GFJ1H8vh7R87L+LtI42rDSqheYNZZU EwY13MXPag7KIO9mt+dX7mVFZBNm3ECIThxuciVKXcGN1YT0Q+mN1G2F3gOH6qYe7VOC F6ow== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1783342675; x=1783947475; h=content-transfer-encoding:mime-version:user-agent:references :in-reply-to:subject:cc:to:from:message-id:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=hO5ho4KeiiLfcBaCI+3UMPtuUVrSULK4qaWn/9TzQms=; b=EbM+D80CFrD5ByqGg8rivkbbdFrb7vjZ2vcJiaK9Yj5I+NTc3qudu7Zc4GwjE58Hp2 FyZb3hZihNGiVNesvU3FObFraAo4XURqOPD37GEnvwBTlC/P+r4R9X7/zrENYrWD0GXv G4rxGa+pHC4rk2EZu/vpO3LNyA014EcF9a2Gq+xq/WpHvxZ2sHSDKGM4NyL0APA28sR+ 0s5IpRIIAkjm+DdU/88lTUGqCrLqa5vBp0n8Kn8GjxLO0fVNS+SCe3xAQ9K5TAJNkU5I Rl77lBtcFgOpQi1p5FCqPvdxEc8DM7Owj/ct30FGxPHGfvfBcoZWNxYT6MqKJvmEMtIX oeGQ== X-Forwarded-Encrypted: i=1; AHgh+RoB6D/+oRWSQbXqoocsg4LEBos4mrNh4v72gfPnHFkTYWtXCJrWrMkZ9wPeQ4q9+h4YNVmJI5UkSg==@kvack.org X-Gm-Message-State: AOJu0YzdIdI/ikNb72A/o9KXkJuHquk/ZE7r5y+MTfEZp/kL+tNjnTAw X9pvO3bh/dkRzUloBeRoh+JV/7LOrC4Btp5TtFW+0fL74dSfxBR/ee1Q X-Gm-Gg: AfdE7cnY/WaU0PWlNNLKX+aJjec1zYjRJyfYvYGcREuUN2o1kYxX5iZxdW7Rb87o/Qb VudO4WShNCCCsDvinVQ6HaBVnlWV3garOLKQ/pyvnJEVOKzXPUxEyp/uFuBrMa1zk9C6hOBC/lp P1MUAnCvSh/rtek4/Qkxx/ks9lsMd/xD4KUKme4b7cZAl0LVO9jCeovU4SWcgLjaxn1gnnA1U1o wbyJ2LiupaVWVeNnIl0apEhZ2sgirUtX86UwZN39POHN47Lvwot6hci20EToc3/hhZmp/5NjVdB BQKB52SvzK+TAqk3BvF97kPkzx3njatvWSeJQzQmMbURU+F6fSPVvf/yKQr6iN3DEeStVttQVqK qq9ET6TH9e0xTxhzn04VHIxgdxeWjWd422FfdCEUQwzQyBU/mBbRrp7S2JsYqgML6Kx4squl7wx jYUW6tjhrfCF5zdbVvjdaGYUbsMvY/XtYBkC42SR5Sjzag1DJRquQbWqakn4mxQnY92UuOOmMuQ rt1PFI7/YqP/1TeQI3hXqenbbdDx1HrsHyNmiDIWh0O X-Received: by 2002:a05:6a21:a91:b0:3b5:530d:d96d with SMTP id adf61e73a8af0-3c08e6b4b43mr515293637.12.1783342675118; Mon, 06 Jul 2026 05:57:55 -0700 (PDT) Received: from mars.local.gmail.com (221x241x217x81.ap221.ftth.ucom.ne.jp. [221.241.217.81]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c9e8f5c175dsm6341551a12.11.2026.07.06.05.57.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 06 Jul 2026 05:57:54 -0700 (PDT) Date: Mon, 06 Jul 2026 21:57:51 +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=ISO-8859-7 Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 74FC74000B X-Stat-Signature: 1mo8asabmca8zb74xrx6me4o58gfewkk X-HE-Tag: 1783342676-301183 X-HE-Meta: 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 XhpDGBD6 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 06 Jul 2026 20:51:36 +0900, Lorenzo Stoakes wrote: >=20 > On Mon, Jul 06, 2026 at 10:27:43AM +0200, Geert Uytterhoeven wrote: > > Hi Andrew, > > > > On Mon, 6 Jul 2026 at 07:23, Andrew Morton = wrote: > > > On Mon, 6 Jul 2026 04:58:28 +0100 Matthew Wilcox wrote: > > > > On Sun, Jul 05, 2026 at 03:27:08PM -0700, Andrew Morton wrote: > > > > > Thanks. Unfortunately we aren't very diligent about the nommu co= de > > > > > (are we?). Perhaps appropriately - clearly this code doesn't ge= t used a > > > > > lot. > > > > > > > > Should we delete support for NOMMU? As you say, it doesn't get much > > > > testing, or presumably usage. I have this quote from #m68k a coupl= e of > > > > years ago... > > > > > > Greg is busily developing kernel code. > > > > > > > : I looked at nommu very briefly when I had my 68000 board on the b= ench > > > > : but didn=A2t get anywhere. Also didn=A2t try particularly hard. I= think > > > > : you are better off with fuzix or OS9 if you want something unixy. > > > > > > > > (i suspect Zephyr would also be good, but it doesn't support m68k, = just > > > > arc, arm, arm64, mips, openrisc, renesas rx, riscv, sparc, x86 and = xtensa) > > > > > > Greg, how mush use is NOMMU Linux seeing nowadays? > > > > Nommu (SH-compatible J-Core ASIC) is used in actual products, running > > modern kernels. The rationale is low interrupt latency without using > > a much more costly app CPU core + RT CPU core split. > > > > Please watch the recording of the "32bit and-or noMMU Linux BoF"[1] > > at LPC2025 for more info. >=20 > This crops up now and again and people point to uses, but fails to addres= s the > real issue here. >=20 > Nobody (aside from Hajime - thank you!) who uses nommu maintains or contr= ibutes > to it, or _even tests_ it as far as I can tell. >=20 > We broken nommu for a year I think it was? And there wasn't one report. >=20 > The last time I raised this, I was admonished and told there are critical= arm32 > nommu devices that absolutely _must_ have the latest kernel and this is > perfectly working code. >=20 > And riscv also introduced (and I'm so very surprised Linus allowed it) a = brand > new nommu architecture (!!) >=20 > And yet... >=20 > If this is really so important, can those who care perhaps help out a bit= ? At > least with testing? >=20 > I'm a bit fed up of it really. >=20 > As far as hobbyist retro stuff and upstream goes, I am sympathetic, I cam= e from > being a hobbyist (though not retro), and would be one again if I couldn't= do it > as a job. >=20 > But retro people do NOT need the latest kernel. As far as I'm concerned, = museum > piece support should be ripped out, and those who care run downstream ker= nels. >=20 > As for the 'critical products' that must use nommu - PLEASE start > contributing. Please start testing. Anything. >=20 > Again thank you Hajime for doing the one thing that really counts here - > contributing to the nommu code. >=20 > Anyway, as to what Matthew said - 100% I am for us ripping it out. >=20 > But it's not up to me, and unfortunately I think we'll get a clammer of v= oices > saying how important it is, and silence again when it comes to do any of = the > work. 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, 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). # 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. 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. 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. I hope this helps a bit. *1 https://lore.kernel.org/all/cover.1770170302.git.thehajime@gmail.com/ *2 https://lore.kernel.org/ltp/20240105131135.GA1484621@pevik/ -- Hajime