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 AE8C6D68BD5 for ; Sun, 21 Dec 2025 09:30:38 +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=wdDZF3/HSZmlH2rDLNptQ5LWR2buABlOXa4bjb4WrgE=; b=xx8swZTZlgF1zkjzvxVB8KuM4K YzToYfV9fikzyIH0dtTjo9wIA1sX59R0gV0HD5HnWtYEtKepRCej12uMk8uKo6iDPAifL9toJ/m7u Lr+CjTOMNmXrhbe5CpbDpdQQyKo5dsh4ZqLX/OGsJPz5fqSVOUaO0AsRluAsTJ0oY4V4Pl0PwtXE7 WP15sCNQZOtPIbP2PKA8g6qosvxodtKn4SpVkiegN6RifXQyLA/cREjesN0u/SmotdcXbZgZ0ptF8 cWTeKuem54NhuLsUYYD6/tdWZTc02BPNRyAntH5vgWiuhG5KtyBLuJS15246RBzdCCDtJcPQc7KMN PwV88O0w==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vXFll-0000000CHZl-20gH; Sun, 21 Dec 2025 09:30:29 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vXFli-0000000CHZL-2OOI for linux-arm-kernel@lists.infradead.org; Sun, 21 Dec 2025 09:30:27 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 44D78436EB; Sun, 21 Dec 2025 09:30:25 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 84754C4CEFB; Sun, 21 Dec 2025 09:30:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1766309425; bh=dynri6cO7Epp0o2N9qQ3cdoFscVQqJSuLqeok3MBBiM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=aZt8jayi0KTKlYfeM8PXcjFeXS/nexnOlW7wp5qpXy8jeA90IS+dY96x2qy1rT5xO FHl5hVlhatmZm8PdARiR984pcX5Xnvb/DN3H8anneFIS8urkPCN+tf5dstcWVRW0gb MtpipYZ4/nTh4uvDJud/EwfAeYoY6eMvezzyrEHIwa4jQVN+kGDWFX9QlrkXMmlhHg +/MzLZJiX1cgSGhR6cIHSoivnfh4RJpQU3BWUmReDCQIKKfO8emvBUqYksawYAEan6 IemtDz7JnMnQaHpRMNWXo27R+S6bUs2yHEAc+/muXldZEic5H52t16UN2Lx8FHINn3 pxRdGiibDmVHQ== Message-ID: <4aecb94f-e283-4720-96e5-1837352c3329@kernel.org> Date: Sun, 21 Dec 2025 10:30:15 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/4] arch/*: increase lowmem size to avoid highmem use To: Dave Hansen , Arnd Bergmann , Arnd Bergmann , linux-mm@kvack.org Cc: Andrew Morton , Andreas Larsson , Christophe Leroy , Dave Hansen , Jason Gunthorpe , Linus Walleij , Matthew Wilcox , Richard Weinberger , Russell King , linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Michal Simek , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Nishanth Menon , Lucas Stach References: <20251219161559.556737-1-arnd@kernel.org> <20251219161559.556737-2-arnd@kernel.org> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251221_013026_656963_FE53BDDB X-CRM114-Status: GOOD ( 17.65 ) 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 12/19/25 21:52, Dave Hansen wrote: > On 12/19/25 12:20, Arnd Bergmann wrote: >>> For simplicity, I think this can just be: >>> >>> - default VMSPLIT_3G >>> + default VMSPLIT_2G >>> >>> I doubt the 2G vs. 2G_OPT matters in very many cases. If it does, folks >>> can just set it in their config manually. >>> >>> But, in the end, I don't this this matters all that much. If you think >>> having x86 be consistent with ARM, for example, is more important and >>> ARM really wants this complexity, I can live with it. >> Yes, I think we do want the default of VMSPLIT_3G_OPT for >> configs that have neither highmem nor lpae, otherwise the most >> common embedded configs go from 3072 MiB to 1792 MiB of virtual >> addressing, and that is much more likely to cause regressions >> than the 2816 MiB default. >> >> It would be nice to not need the VMSPLIT_2G default for PAE/LPAE, >> but that seems like a larger change. > > The only thing we'd "regress" would be someone who is repeatedly > starting from scratch with a defconfig and expecting defconfig to be the > same all the time. I honestly think that's highly unlikely. > > If folks are upgrading and _actually_ exposed to regressions, they've > got an existing config and won't be hit by these defaults at *all*. They > won't actually regress. > > In other words, I think we can be a lot more aggressive about defaults > than with the feature set we support. I'd much rather add complexity in > here for solving a real problem, like if we have armies of 32-bit x86 > users constantly starting new projects from scratch and using defconfigs. > > I'd _really_ like to keep the defaults as simple as possible. I agree with that. In particular in areas where there is the chance that we could count the number of people that actually care about that with one hand (in binary ;) ). -- Cheers David