From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from blackbird.sr71.net (blackbird.sr71.net [198.145.64.142]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2062E1E520A; Wed, 10 Sep 2025 16:42:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.145.64.142 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757522575; cv=none; b=L1UnL2gEioC5hDPxhvaw2uhJ3e4KTS4QvJ36GpXpoGh0eei8BMoADOYYJ4fm4YLeBSj6twzUJq77+ZJENSgx4cTIwaKOpvWxUqm7giempYHwqyseuQO64IDeQN1cX4fJWWmXrJYAXIpLSMQQknf4Bjvp339CpYU75Remy9VdxsA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757522575; c=relaxed/simple; bh=ioGpMBeXdAlS89t3hTLb2V4iRQeQROs5/oUBcEzBldg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=sKb/SGIDdUYo0ZYnrqmuCsDnrYwmoYFPRbapSMyUaQF2+nZoYqTPCrJMli0mgc0hInxG5HFM3S1jGpYpQE/EPhigLFWvrj7ysiicvkGmr+KtPko/RAXiTuPflyHGHKeHDBO/sbHAyYS8JB5wUTaj2+SNztjkJY4AmofFv0fELnQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=sr71.net; spf=pass smtp.mailfrom=sr71.net; arc=none smtp.client-ip=198.145.64.142 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=sr71.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=sr71.net Received: from [0.0.0.0] (unknown [134.134.139.69]) (Authenticated sender: dave) by blackbird.sr71.net (Postfix) with ESMTPSA id 4234E20193; Wed, 10 Sep 2025 09:34:45 -0700 (PDT) Message-ID: Date: Wed, 10 Sep 2025 09:34:43 -0700 Precedence: bulk X-Mailing-List: ksummit@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [TECH TOPIC] Reaching consensus on CONFIG_HIGHMEM phaseout To: Richard Weinberger , Arnd Bergmann Cc: ksummit , linux-kernel , linux-arm-kernel , linuxppc-dev@lists.ozlabs.org, linux-mips , linux-mm , imx@lists.linux.dev, Christophe Leroy , Lucas Stach , Linus Walleij , Geert Uytterhoeven , Ankur Arora , David Hildenbrand , Mike Rapoport , Lorenzo Stoakes , Matthew Wilcox , Andrew Morton , "Liam R. Howlett" , vbabka , Suren Baghdasaryan , Ira Weiny , Nishanth Menon , heiko , Alexander Sverdlin , "Chester A. Unal" , Sergio Paracuellos , Andreas Larsson References: <4ff89b72-03ff-4447-9d21-dd6a5fe1550f@app.fastmail.com> <497308537.21756.1757513073548.JavaMail.zimbra@nod.at> From: Dave Hansen Content-Language: en-US In-Reply-To: <497308537.21756.1757513073548.JavaMail.zimbra@nod.at> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/10/25 07:04, Richard Weinberger wrote: > I am part of a team responsible for products based on various 32-bit > SoCs, so I'm alarmed. These products, which include ARMv7 and PPC32 > architectures with up to 2 GiB of RAM, are communication systems > with five-figure deployments worldwide. > > Removing high memory will have an impact on these systems. The > oldest kernel version they run is 4.19 LTS, with upgrades to a more > recent LTS release currently in progress. We typically upgrade the > kernel every few years and will continue to support these systems > for at least the next 10 years. > > Even with a new memory split, which could utilize most of the > available memory, I expect there to be issues with various > applications and FPGA device drivers. I'd be really curious what the _actual_ issues would be with a non-standard split. There are a lot of "maybe" problems and solutions here, but it's hard to move forward without known practical problems to tackle. Has anybody run into actual end user visible problems when using one of weirdo PAGE_OFFSET configs?