From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-out3.simply.com (smtp-out3.simply.com [94.231.106.210]) (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 A65FD23E23C; Thu, 11 Sep 2025 05:38:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=94.231.106.210 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757569113; cv=none; b=u1DIdvl4dPpLIU5wLQd60iH3/R9AMMq96/zWygl4ceJt5VgAOKySKNo+EGYgcMqdGdsxYyOUzKo1VYcBvn2Ks7qN4ten0xWAdBgfxst/Y7lCMh9M/HUvZTEN56Rs16L2c7GjgyrwgHlqUAxvKRsR0z6EkCNoD0kkT892v559tG4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757569113; c=relaxed/simple; bh=zslq5NZ9GBE+NFMFpUXQKdQwmGpJdU16zodzEZ5lWJ8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=amjmZjD/VqyCfyUaPsiybHxCKnJ6r+099qVDEe+S9L5okhWZoBiwOgsbyIjNy8Mvw+npb30PztVdVA8sDONAE40P7Lx03z/RgV6chsFn+jI2CzfSGDAG6nklNWJLogLuNCTnMv146jJPf/ci0GYVn1UHhZ8lqpgAjV1msJButn8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gaisler.com; spf=pass smtp.mailfrom=gaisler.com; dkim=fail (0-bit key) header.d=gaisler.com header.i=@gaisler.com header.b=Hs7ZfSyD reason="key not found in DNS"; arc=none smtp.client-ip=94.231.106.210 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gaisler.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gaisler.com Authentication-Results: smtp.subspace.kernel.org; dkim=fail reason="key not found in DNS" (0-bit key) header.d=gaisler.com header.i=@gaisler.com header.b="Hs7ZfSyD" 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org 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: 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 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