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Fri, 19 Dec 2025 15:20:40 -0500 (EST) X-Mailer: MessagingEngine.com Webmail Interface MIME-Version: 1.0 X-ThreadId: AhgucsMdbVXw Date: Fri, 19 Dec 2025 21:20:20 +0100 From: "Arnd Bergmann" To: "Dave Hansen" , "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" , "David Hildenbrand (Red Hat)" , "Lorenzo Stoakes" , "Liam R. Howlett" , "Vlastimil Babka" , "Mike Rapoport" , "Suren Baghdasaryan" , "Michal Hocko" , "Nishanth Menon" , "Lucas Stach" Message-Id: In-Reply-To: References: <20251219161559.556737-1-arnd@kernel.org> <20251219161559.556737-2-arnd@kernel.org> Subject: Re: [PATCH 1/4] arch/*: increase lowmem size to avoid highmem use Content-Type: text/plain Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: BA7F2180016 X-Rspamd-Server: rspam04 X-Stat-Signature: 3on9s6ysw9eigjo4daxbbbrss76179ni X-HE-Tag: 1766175645-710064 X-HE-Meta: U2FsdGVkX1+CkfNbLGjMiC8IcG6KCrnD8UbSW9G3tE7xd2ZC/Mk6IeJZ+bb1Q6f2bs56DbaSANNHNTigUzBPIvdlXbMD6haZRHvNQ5BNeSzXSAYr9PpaLi68z9Mbz3REkgdiLrWrvdxoIgnEVc6bYZ2USuEPxaWQ49QNFEF63xFzi4uRebKWmkmtOb+W4F8skWNOa+5qQd6YsikMzfiSU3iqcs8WYj1aTSr/h9T276eADVg3vBVQjvSnLCXqcms4DY3aLNitMBdDNjf5py/h10WdmACbx3S9qTxuvZKfcAXzE37O19QyNfN7TCSTaR2Y42TPCl+tPyxT/fcMQO9fwv3YiYV5EZnFV3UUDjNsX3SDoJrPw6g5kM8zeJIY6ci+qXzfwuOKeFr1mrD4yohj79DibWwMaroks/d8MIXL4b8Xn8vUkISZgq/nQjM5A0M56B/Diqezl7BRah0f1bb5efWjSJT6PY3ULUAXJqKpsDD8NPn4cvZG5ZlVvxmhlWcCay75YBAGqsm2RLWZCKMwoXLkM7/Qz4HuW/1N/vGd8NNZqxvWN12ZsMi6UGRUiE7I95FelUVg1kEF+DkZdpe5uneZoxyLa9mxv62xaiMNAFu7ZJ+1hPAeiLTBjxOerRF/stc8ME9h/UDh8Oej6PV/Oy231uVKZtaYW2x3AQ/l31xoZB6wg2QEP6bMvEfHr4/kNlPOUiq7Wx3Qlu9FKRDx+HTU4Y9ZpBABMg52gEdaE3Kd+xqLIgGSdznS0FlNSP6n0GdDcRHHIeMUyyOD6UZJoYpFL1gYvKLkEufH4MCyRnfW1lEip5IzKZXVQsiFcU3od98fPMvgdmHzEcpHkJzP7KKK+zDu3z15Z/ryc4TxF/hQJj46ACPDIPgNSXCllHN6Zw/V6t++w9fK9Ly0qEWAXCVA4jp5XHuI1nTrLjdfu6HZJRD6sKINiwpPkH55TbVrG9tnb/DcWFy+iwlSkyX ihCfLXJB gFU81AsUKQnLrFVI3krQKBbnmzBG0DH0F7r9G+p43iW5TnMsZcmzQWM+ZgTzcvgrMcEz/66U9qxlYJrlume9HTrjRoAZSo+BpU9b5XaJjCwliqPnRAuXXFy2J/HB3LHwkqIkBM9Hr0oBxRcA+NlMRQaCF+AUfHpYLDAjQShgzy8n9SzKiKmDLkRjPvSWGGzNWucLMMhOJtci84b9albGlCysGeFe+Zkj8uFJx X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Dec 19, 2025, at 19:02, Dave Hansen wrote: > On 12/19/25 08:15, Arnd Bergmann wrote: >> --- a/arch/x86/Kconfig >> +++ b/arch/x86/Kconfig >> @@ -1416,7 +1416,9 @@ config HIGHMEM4G >> >> choice >> prompt "Memory split" if EXPERT >> - default VMSPLIT_3G >> + default VMSPLIT_2G_OPT if HIGHMEM && !X86_PAE >> + default VMSPLIT_2G if X86_PAE >> + default VMSPLIT_3G_OPT >> depends on X86_32 > > 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. Arnd