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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 6C203CA0FED for ; Wed, 10 Sep 2025 14:04:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:MIME-Version:Subject:References:In-Reply-To:Message-ID:Cc:To: From:Date:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=XGf6An9pkuacotas4PAUho44h/2LaY9ZaYpivcI6rZY=; b=cAUpLeVh1qko8JEplDqxExlSKQ 6kVoBZKNyQo3yZsa0ZC0o9mPjt1xIyZwbT3YV96Mft+2qQ652XOH1NHx/dfRYi6fIDaTsrm+5Akj8 c8MDPqTxdVhro1L0zpEkNZbFir7gF1pQ4uMvjlojHkaNiXmFUrT/h4PGURreXGfN70YFx2v/Rs3/w 92fDH36XesRd24Zj/XGWNdg+Cqnsb3AYKpSOiFRzGJVVTHgC0jrMh59zgk4c4zPHMR/0aO3/VOa6w v5yXl8P6gtqjumyEumdiRW09dIJETJrc3Rlto85rNtU+J6ys7CHY4bpIflK2hMndzAYN8DZmZLt5C cZ1zx+Jg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uwLRB-0000000EZUA-2lbS; Wed, 10 Sep 2025 14:04:41 +0000 Received: from mailout.nod.at ([116.203.167.152] helo=lithops.sigma-star.at) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1uwLR8-0000000EZPt-0xYE for linux-arm-kernel@lists.infradead.org; Wed, 10 Sep 2025 14:04:40 +0000 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 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Originating-IP: [195.201.40.130] 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== X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250910_070438_554582_AA03003D X-CRM114-Status: GOOD ( 20.67 ) X-BeenThere: linux-arm-kernel@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-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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