From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lithops.sigma-star.at (mailout.nod.at [116.203.167.152]) (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 6B121322A13; Wed, 10 Sep 2025 14:04:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=116.203.167.152 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757513079; cv=none; b=O9H+l6jPiTAmJGF55PhinCezCRCqTuQknDoUHW+L3yV38PwVzgMr8pKQaYGiSBe7JytqEtbqofe22urcCXVi1pgA5bu+2Rfc5hxZIYYfqBCWzQnwc4MOnZZv9eYxjIzBmecWwQ4hxIWh4Kxr3VeWbwkCemGjD+nlBwuo/DcTj2w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757513079; c=relaxed/simple; bh=XGf6An9pkuacotas4PAUho44h/2LaY9ZaYpivcI6rZY=; h=Date:From:To:Cc:Message-ID:In-Reply-To:References:Subject: MIME-Version:Content-Type; b=ImeF2pWs+rxRZD+RH7GPQCw6PA1bR1Y/WmYNzejVqQxGNx9uwyIvTJ3L5V7hD3GBdvOo49PYLSDkOB5inOrZ+n99e0IaAHF3ja3IAAUzhklQo6QqPapgh5XYre/89MyDGYQcX/3zf110wdG/4QlX7J8shgfnMo3lxMbaqWadDiE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=nod.at; spf=fail smtp.mailfrom=nod.at; arc=none smtp.client-ip=116.203.167.152 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=nod.at Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=nod.at Received: from localhost (localhost [127.0.0.1]) by lithops.sigma-star.at (Postfix) with ESMTP id D2E8683E14; Wed, 10 Sep 2025 16:04:34 +0200 (CEST) Received: from lithops.sigma-star.at ([127.0.0.1]) by localhost (lithops.sigma-star.at [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id LaIcEPcDfBsv; Wed, 10 Sep 2025 16:04:34 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by lithops.sigma-star.at (Postfix) with ESMTP id 1A4472FFDA5; Wed, 10 Sep 2025 16:04:34 +0200 (CEST) Received: from lithops.sigma-star.at ([127.0.0.1]) by localhost (lithops.sigma-star.at [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id X4a51J5LvQXj; Wed, 10 Sep 2025 16:04:33 +0200 (CEST) Received: from lithops.sigma-star.at (lithops.sigma-star.at [195.201.40.130]) by lithops.sigma-star.at (Postfix) with ESMTP id C16AD83E14; Wed, 10 Sep 2025 16:04:33 +0200 (CEST) Date: Wed, 10 Sep 2025 16:04:33 +0200 (CEST) From: Richard Weinberger To: 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 Message-ID: <497308537.21756.1757513073548.JavaMail.zimbra@nod.at> In-Reply-To: <4ff89b72-03ff-4447-9d21-dd6a5fe1550f@app.fastmail.com> References: <4ff89b72-03ff-4447-9d21-dd6a5fe1550f@app.fastmail.com> Subject: Re: [TECH TOPIC] Reaching consensus on CONFIG_HIGHMEM phaseout Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Mailer: Zimbra 8.8.12_GA_3807 (ZimbraWebClient - FF141 (Linux)/8.8.12_GA_3809) Thread-Topic: Reaching consensus on CONFIG_HIGHMEM phaseout Thread-Index: xOQifXk0CYTOSYO4gO/z6lk9BLmNXg== Arnd, ----- Urspr=C3=BCngliche Mail ----- > Von: "Arnd Bergmann" > High memory is one of the least popular features of the Linux kernel. > Added in 1999 for linux-2.3.16 to support large x86 machines, there > are very few systems that still need it. I talked about about this > recently at the Embedded Linux Conference on 32-bit systems [1][2][3] > and there were a few older discussions before[4][5][6]. >=20 > While removing a feature that is actively used is clearly a regression > and not normally done, I expect removing highmem is going to happen > at some point anyway when there are few enough users, but the question > is when that time will be. >=20 > I'm still collecting information about which of the remaining highmem > users plan to keep updating their kernels and for what reason. Some > users obviously are alarmed about potentially losing this ability, > so I hope to get a broad consensus on a specific timeline for how long > we plan to support highmem in the page cache and to give every user > sufficient time to migrate to a well-tested alternative setup if that > is possible, or stay on a highmem-enabled LTS kernel for as long > as necessary. 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 Gi= B 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 rec= ent LTS release currently in progress. We typically upgrade the kernel every few years and will continue to suppor= t these systems for at least the next 10 years. Even with a new memory split, which could utilize most of the available mem= ory, I expect there to be issues with various applications and FPGA device drive= rs. Thanks, //richard