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 38D52CAC583 for ; Thu, 11 Sep 2025 05:38:40 +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:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=J4SmUX7P+kpNB7OaZvmmYUNeRGLdLLWkUbpUICDS3qY=; b=2/Saei7cuQWM/BngWPKNrXw2bz VBvAOEsVw3nD4yY10zKYuhk2HSGK+xwFXgWbMqSTO64VKmzeks7Adm1VWfAH9goCFFAjeJNa+bb0H kkeA1qZuFz1hR764lbeJPofFGSsU3IM0iB2PDenKWGR7b/FaZC/qOqzQohaZwbH8L9IkbsYtqcpq+ dZwLKKmlkxYfkbdmBZq+v1G24lOpHVJarlgGDUhybRnPc/51Z9hIpvuuz04wKT7H0kpau1/z7qSUy xrmTrb9F3rwbzi7yjEsc3NvU7vuXOgEv0wD2BF8eSX/6aDeoBgMvT3SGHDf89ItWQYkOzxQn9+d87 wsfOs0EA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uwa0t-000000012bl-0tk5; Thu, 11 Sep 2025 05:38:31 +0000 Received: from smtp-out3.simply.com ([94.231.106.210]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1uwa0p-000000012XP-2f5D for linux-arm-kernel@lists.infradead.org; Thu, 11 Sep 2025 05:38:29 +0000 Received: from localhost (localhost [127.0.0.1]) by smtp.simply.com (Simply.com) with ESMTP id 4cMmYn6jWzz1FQVw; Thu, 11 Sep 2025 07:38:21 +0200 (CEST) Received: from [192.168.0.25] (h-98-128-223-123.NA.cust.bahnhof.se [98.128.223.123]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (Client did not present a certificate) by smtp.simply.com (Simply.com) with ESMTPSA id 4cMmYn1PXCz1FQVP; Thu, 11 Sep 2025 07:38:21 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gaisler.com; s=simplycom2; t=1757569101; bh=J4SmUX7P+kpNB7OaZvmmYUNeRGLdLLWkUbpUICDS3qY=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Hs7ZfSyDOM7aPRu33LOA+3yef+fVto4kU9xa+4YpClIxfuXs1fUOvHNHSbYzTsH95 ys3zgWHJHS23RTioc6nK1rRkrbxCam9D5ptr5a/DgIz7xpPRDCQ6Etyd5bStpWc73w 7yOC/+8Ounc2FdB1AGu5KYNtNxw+XWF0Y0vJdIXiwXVxxPzwE6FGqoMLKjGAvRTDu6 0tRpQ6v9KDjievFY3f8w6p8LSH1LMGdoj0SQczd00LYltcWoPmKILRmn5F8FOypXFd 6Zp6gO/YqFuyTXHhSNlsS6DU3Zk+NRltjlY23ffJsltCzkH4eal4Sp3ahPCc/wsqRM gmrx1Brnia8oQ== Message-ID: <5d2fec2b-8e59-417e-b9e6-12c6e27dd5f0@gaisler.com> Date: Thu, 11 Sep 2025 07:38:15 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [TECH TOPIC] Reaching consensus on CONFIG_HIGHMEM phaseout To: Arnd Bergmann , ksummit@lists.linux.dev Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, imx@lists.linux.dev, Christophe Leroy , Richard Weinberger , Lucas Stach , Linus Walleij , Geert Uytterhoeven , Ankur Arora , David Hildenbrand , Mike Rapoport , Lorenzo Stoakes , Matthew Wilcox , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Suren Baghdasaryan , Ira Weiny , Nishanth Menon , =?UTF-8?Q?Heiko_St=C3=BCbner?= , Alexander Sverdlin , "Chester A. Unal" , Sergio Paracuellos References: <4ff89b72-03ff-4447-9d21-dd6a5fe1550f@app.fastmail.com> Content-Language: en-US From: Andreas Larsson In-Reply-To: <4ff89b72-03ff-4447-9d21-dd6a5fe1550f@app.fastmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250910_223828_046264_55C51ADB X-CRM114-Status: GOOD ( 19.05 ) 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 On 2025-09-09 23:23, Arnd Bergmann wrote: > 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]. > > 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. > > 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. We have a upcoming SoC with support for up to 16 GiB of DRAM. When that is used in LEON sparc32 configuration (using 36-bit physical addressing), a removed CONFIG_HIGHMEM would be a considerable limitation, even after an introduction of different CONFIG_VMSPLIT_* options for sparc32. Regards, Andreas