On Tue, Apr 16, 2024 at 07:19:27PM +0300, Mike Rapoport wrote:
> > "last page of the first gigabyte" - why first gigabyte? Do you mean
> > last page of *last* gigabyte?
>
> With 3G-1G split linear map can map only 1G from 0xc0000000 to 0xffffffff
> (or 0x00000000 with 32-bit overflow):
>
> [ 0.000000] lowmem : 0xc0000000 - 0x00000000 (1024 MB)
.. but you can't map that much. You need to reserve space for (may not
be exhaustive):
- PCI BARs (or other MMIO)
- vmap
- kmap
- percpu
- ioremap
- modules
- fixmap
- Maybe EFI runtime services?
You'll be lucky to get 800MB of ZONE_NORMAL.