On 2024-03-06 19:19, Arnd Bergmann wrote: > On Wed, Mar 6, 2024, at 17:22, Arnd Bergmann wrote: >> On Wed, Mar 6, 2024, at 16:31, Andreas Larsson wrote: > >> On a relate note, it does seem odd to have such a small >> lowmem area, and I wonder if that could be extended. >> The 192MB lowmem limit comes from >> >> #define SRMMU_MAXMEM 0x0c000000 >> >> but I don't understand if that is a hardware limitation >> or a design choice that can be changed, and if it is >> even valid on leon or only on the old sun machines. > > I had another look and found that this is a result of > > arch/sparc/include/asm/page_32.h:#define PAGE_OFFSET 0xf0000000 > > which gives 3840MiB to userspace addresses, leaving only > 256MiB for kernel lowmem and vmalloc space, which is > less than any other architectures. > > I still don't know the history behind this choice, but I > see this was already configured the same when arch/sparc/ > was originally merged. You can probably change it to a more > sensible 0xc0000000 or 0x80000000 like on other > architectures and run without highmem on anything with > less than 2GB of total RAM. > > How much RAM do Leon machines have typically, or at the > maximum? The amount of RAM can vary greatly between systems, from less that 128 MiB up to 2 GiB. An upcoming design uses the entire 36-bit physical address space and have the possibility of having up to 60 GiB memory. Thanks, Andreas
