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]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4E15CD78764 for ; Fri, 22 Nov 2024 09:53:27 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BC7938D0008; Fri, 22 Nov 2024 04:53:26 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id B79608D0007; Fri, 22 Nov 2024 04:53:26 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A3E078D0008; Fri, 22 Nov 2024 04:53:26 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 83B168D0007 for ; Fri, 22 Nov 2024 04:53:26 -0500 (EST) Received: from smtpin09.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 3BF1514116D for ; Fri, 22 Nov 2024 09:53:26 +0000 (UTC) X-FDA: 82813265388.09.8923369 Received: from sipsolutions.net (s3.sipsolutions.net [168.119.38.16]) by imf09.hostedemail.com (Postfix) with ESMTP id 49A0614000F for ; Fri, 22 Nov 2024 09:52:47 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=sipsolutions.net header.s=mail header.b=NAzjrDFk; spf=pass (imf09.hostedemail.com: domain of johannes@sipsolutions.net designates 168.119.38.16 as permitted sender) smtp.mailfrom=johannes@sipsolutions.net; dmarc=pass (policy=none) header.from=sipsolutions.net ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1732269111; 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=KqKwG87BOhNBp9dKTgOo7Io++iQzzo3AhB7LBoi2ljU=; b=o4jkCyH6l08GqlIDIwI8PBQBd4DaVbAzX5c3j5BTgtdZTSoehn/3wKDz/bo/LBN4bKVMe6 IjxLgdqa5AfIdfmGSDCewEu9RcARY4O/7c5wf9ZB7xxv+Zv9ML6wTMDAEXD6YzYEN/tYLr yNfv+xrVdxO4QN+wD1E69misV99t5O8= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1732269111; a=rsa-sha256; cv=none; b=ePjbrWRAwJfGlD/IZbrrEt5LtB+3q+8sdKVq8huoV8P0MrZUE3LfhhlNOz5r5/O4ToI5PD CkZLbkenqySdw6v58ZceMeXsw0qGMv+0ILRYySf84k0TV+mzs+GFTUTiPwJvdPJtSpQg16 YfTQEcMiewzMPOM/kU8tFbfVu+l9y+E= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=pass header.d=sipsolutions.net header.s=mail header.b=NAzjrDFk; spf=pass (imf09.hostedemail.com: domain of johannes@sipsolutions.net designates 168.119.38.16 as permitted sender) smtp.mailfrom=johannes@sipsolutions.net; dmarc=pass (policy=none) header.from=sipsolutions.net DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sipsolutions.net; s=mail; h=MIME-Version:Content-Transfer-Encoding: Content-Type:References:In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender :Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From:Resent-To: Resent-Cc:Resent-Message-ID; bh=KqKwG87BOhNBp9dKTgOo7Io++iQzzo3AhB7LBoi2ljU=; t=1732269204; x=1733478804; b=NAzjrDFkq3BGhAGeUJ2c1z1aikHfYRR3RQTfv6pPW2ltPEJ Ve7IPLKUPUsgAF06stZgfAuJath+9iRBTFmngQq/TAyielq4hczkoXK2IUV+5568r5gH3VIf7sbpr pW3jkGXCaWT7u+RD4W/wLpU16G4hTLjUAbhAwyC0195U3X1lD2SJkMH/yjhKexXrc3ro4gvsj/Og0 io2ZmATw2oheSqH9meU3lCIa+v62HynmPMeLQeN08Bpsb9AeTlpYyns0Nk2a8BYl5td3c/8iuK8Wg PaVL9S9zLKE1EmjwoGpmAkQ4/ZgKij0yBcvaObn551JPqQoqaFZGmq3Q4t3aZagA==; Received: by sipsolutions.net with esmtpsa (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.98) (envelope-from ) id 1tEQLn-0000000BWH4-1sf6; Fri, 22 Nov 2024 10:53:19 +0100 Message-ID: <0930a0fa8e28ecaf92727229e6633278399409e7.camel@sipsolutions.net> Subject: Re: [RFC PATCH v2 00/13] nommu UML From: Johannes Berg To: Lorenzo Stoakes , Hajime Tazaki Cc: linux-um@lists.infradead.org, ricarkol@google.com, Liam.Howlett@oracle.com, vbabka@suse.cz, linux-mm@kvack.org, Jann Horn , Christoph Hellwig , Damien Le Moal Date: Fri, 22 Nov 2024 10:53:18 +0100 In-Reply-To: <77ab71c7-3608-4636-a618-3044c2316a92@lucifer.local> References: <77ab71c7-3608-4636-a618-3044c2316a92@lucifer.local> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.52.4 (3.52.4-2.fc40) MIME-Version: 1.0 X-malware-bazaar: not-scanned X-Rspamd-Server: rspam10 X-Stat-Signature: e5d5fspfhqfd3k4xgtdqjmfq8enxymsm X-Rspamd-Queue-Id: 49A0614000F X-Rspam-User: X-HE-Tag: 1732269167-130037 X-HE-Meta: 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 qlk8x49D 0/r+NC9M80SXUciMKnLKjKshL8g5VLUgi0gBf4BftuQVNnYno6F81R6rfUf8YecKnLdOOBX+jBbVFQOQ/XFmESCgqjPVjbqZxg9gR2AAPC2wRRaEF5ocmdnVtqeTxNwel6jfAzkKbJakl+aMVVqfvJt8RwuYcp2lTn7tiz5gEgeAFYPLpmhKWDZY4dQvxA4GSkWGov2Ymx63z32gEbuxWhzES7KL/4cj6nErcpkUP/Zq+fuNJyFjfmUR5Nw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 2024-11-22 at 09:33 +0000, Lorenzo Stoakes wrote: >=20 > In general, while I appreciate your work and don't mean to be negative, w= e > in mm consistently have problems with nommu as it is a rarely-tested > more-or-less hack used for very few very old architectures and a constant > source of problems and maintenance overhead for us. >=20 > It also complicates mm code and time taken to develop new features. >=20 > So ideally we'd avoid doing anything that requires us maintain it going > forward unless the benefits really overwhelmingly outweigh the drawbacks. :) There aren't really any benefits to ARCH=3Dum in *itself*, IMHO. > There have been various murmourings about moving towards elimination of > nommu, obviously this would entirely prevent that. No objection from me, but e.g. RISC-V added nommu somewhat recently? (+Christoph, Damien) So we could argue the other way around and say that while we have other architectures with nommu (like RISC-V), having ARCH=3Dum could simplify testing by e.g. allowing a kunit configuration in ARCH=3Dum which is simpler (and probably faster) to run for most people than simulating a foreign architecture. Anyway, I think that's where I am with my partial (and very limited) ARCH=3Dum maintainer role. I don't really care for having the feature in UML itself, but if it's useful for testing nommu architectures for someone else, it doesn't seem too problematic to support. And testing such things is also a big part of the argument Hajime was making, afaict. johannes