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
