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Howlett" , vbabka , Suren Baghdasaryan , Ira Weiny , Nishanth Menon , heiko , Alexander Sverdlin , "Chester A. Unal" , Sergio Paracuellos , Andreas Larsson References: <4ff89b72-03ff-4447-9d21-dd6a5fe1550f@app.fastmail.com> <497308537.21756.1757513073548.JavaMail.zimbra@nod.at> From: Christophe Leroy Content-Language: fr-FR In-Reply-To: <497308537.21756.1757513073548.JavaMail.zimbra@nod.at> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: D4A0940009 X-Stat-Signature: ykpdx9pax9b1spomirm4st9848td9gaz X-Rspam-User: X-HE-Tag: 1757524291-645358 X-HE-Meta: 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 bFIi3A7Y mStiMOLQcjBP88d65uilL2sBWjV6Lvn4oq+dKwCujtRJco/igMlyw+Q5YMcv38YrFemjNiPiFQEcboipQdHyCkmwCpD+AOxXgJPiZXaHp3/cj6d6KV5ELr0sa/ylvFV8lOKXLBGiI05bLHFs46uPmlPMSU2CakgNUQ5yBhHifEQSF4MZhohnnAAhIpjgDkZZP/hS9lxwgtuO+BmUFJ6cKXJ7QR1EbEGbZnUcukTp5xHTiMFsD2rpIJqIkbPUf1IjdCg9DFKE14lYOI4Lgjkl+kMSmj+GPQo30VfrLqRH4ecdSD+SjFFE64IRuU/g819eKbQuicLLjHVPelFxXF1N507sSvkG6tyNrREdaBmX+p/6XlLCMw9APQDHNxCafd9fSFHj6+slrLv2VEbE= 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: Hi Richard, Le 10/09/2025 à 16:04, Richard Weinberger a écrit : > Arnd, > > ----- Ursprüngliche Mail ----- >> Von: "Arnd Bergmann" >> 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. > > I am part of a team responsible for products based on various 32-bit SoCs, > so I'm alarmed. > These products, which include ARMv7 and PPC32 architectures with up to 2 GiB of RAM, > are communication systems with five-figure deployments worldwide. > > Removing high memory will have an impact on these systems. > The oldest kernel version they run is 4.19 LTS, with upgrades to a more recent > LTS release currently in progress. > We typically upgrade the kernel every few years and will continue to support > these systems for at least the next 10 years. > > Even with a new memory split, which could utilize most of the available memory, > I expect there to be issues with various applications and FPGA device drivers. Can you tell which PPC32 model/family you are using ? Is it mpc85xx or and/or other variants ? Maybe we can look at keeping CONFIG_HIGHMEM or find alternatives for that subset of PPC32 only. Could you also elaborate a bit on the kind of issues you forsee or fear with applications and FPGA device drivers. FWIW I sent out today a patch that removes CONFIG_HIGHMEM complely on powerpc in order to get a better view of the impacted areas and allow people to test what it looks like on their system without CONFIG_HIGHMEM. See [1]. Christophe [1] https://patchwork.ozlabs.org/project/linuxppc-dev/patch/28d908b95fe358129db18f69b30891788e15ada0.1757512010.git.christophe.leroy@csgroup.eu/