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 0256DCAC582 for ; Fri, 12 Sep 2025 09:59:31 +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:Message-ID:References:In-Reply-To:Subject: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=wXwHzs3cuy4XVADNPAdl5sfqQoJprLOTD7qqu5IX6ek=; b=ZqwdsV/tMSpmNlW5lwAUWHUHJd xiuyDXD9tkjQZLHVcYCPGE7bXRk9GG4BUimjws4YDnNpLZl5bDuKnm9vAwQyvuTXHFzwqq8o2oK2p XMEhLD13JXfh7Z+jO57ODczpdw/TOE9LEq8050wp+MYqLZ2BlNeQMPTLBu+OfLWJBAAiI3XbtmjPC r46xR9nDK+Rtkc+UhEEMBDhuycbuI2WL0Xa72ci33dTzv1/FQOL2UWtOR/TUKk5mWF/D9qfBqNcck 2j+tQw9hYC0voJKL6gGO965v+peI4dSKKubt3Tkm1MbBowmJZMVMsgIYyZRQ5MpSoqsxRXzJK/XnC AXeXR0Kg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1ux0Yy-00000008R6c-3q1I; Fri, 12 Sep 2025 09:59:28 +0000 Received: from terminus.zytor.com ([2607:7c80:54:3::136] helo=mail.zytor.com) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1ux0Yw-00000008R5t-1KvB for linux-arm-kernel@lists.infradead.org; Fri, 12 Sep 2025 09:59:27 +0000 Received: from ehlo.thunderbird.net (c-76-133-66-138.hsd1.ca.comcast.net [76.133.66.138]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 58C9wovj1383935 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Fri, 12 Sep 2025 02:58:50 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 58C9wovj1383935 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025082201; t=1757671132; bh=wXwHzs3cuy4XVADNPAdl5sfqQoJprLOTD7qqu5IX6ek=; h=Date:From:To:CC:Subject:In-Reply-To:References:From; b=Iv4suKXiAxoLsxR2i11aAdvhMLL0LO5cMcs1CvBme2/ey9ISbE8mmgQ2f9bOYVhlv 2l1qElf6X9ZwESTueasD9/lDo017OlrdCm8f2y4ckj3NA9QXf4T5BYDKS6pLCC2hQE 8q+SZy2Dwf91S5hGoA2CP767WUCArqI8deJyBK171k0gbhXOuRszd/TpSl98B8Gicy pmBmXN/1mNCAHsS+pgcVurnG5yieK0YeNEr4nImgCKJ7mZJmOM5odOCX4B0Ck3SN+E blt70msFBUwxUp3/M097HMDT54EEYk5VaHutWeDlQ5yVo3/5b/ggpIM2UrfLYw+JHB /PgINChn3uJzg== Date: Fri, 12 Sep 2025 02:58:48 -0700 From: "H. Peter Anvin" To: Andreas Larsson , 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 , =?ISO-8859-1?Q?Heiko_St=FCbner?= , Alexander Sverdlin , "Chester A. Unal" , Sergio Paracuellos Subject: Re: [TECH TOPIC] Reaching consensus on CONFIG_HIGHMEM phaseout User-Agent: K-9 Mail for Android In-Reply-To: <5d2fec2b-8e59-417e-b9e6-12c6e27dd5f0@gaisler.com> References: <4ff89b72-03ff-4447-9d21-dd6a5fe1550f@app.fastmail.com> <5d2fec2b-8e59-417e-b9e6-12c6e27dd5f0@gaisler.com> Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250912_025926_351448_591E600E X-CRM114-Status: GOOD ( 18.70 ) 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 September 10, 2025 10:38:15 PM PDT, Andreas Larsson wrote: >On 2025-09-09 23:23, Arnd Bergmann wrote: >> High memory is one of the least popular features of the Linux kernel=2E >> Added in 1999 for linux-2=2E3=2E16 to support large x86 machines, there >> are very few systems that still need it=2E 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]=2E >>=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=2E >>=20 >> I'm still collecting information about which of the remaining highmem >> users plan to keep updating their kernels and for what reason=2E 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=2E > >We have a upcoming SoC with support for up to 16 GiB of DRAM=2E 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=2E > >Regards, >Andreas > > It really sounds like a self-inflicted problem=2E=2E=2E getting your custo= mers switched over to the RV64 side is probably the best you can do for the= m=2E