On 10.10.23 02:20, Andrew Morton wrote:

On Sun, 08 Oct 2023 09:54:22 +1100 Michael Ellerman [off-list ref] wrote:

quoted

quoted

I don't know why powerpc's PTE_INDEX_SIZE is variable.

To allow a single vmlinux to boot using either the Hashed Page Table
MMU, or Radix Tree MMU, which have different page table geometry.

That's a pretty crucial feature for distros, so that they can build a
single kernel to boot on Power8/9/10.

Dumb question: why can't distros ship two kernels and have the boot
loader (or something else) pick the appropriate one?

One answer I keep hearing over and over again is "test matrix 
explosion". So distros only do it when unavoidable: for example, when 
differing PAGE_SIZE is required (e.g., 4k vs 64k) or we're dealing with 
RT support (RT vs !RT).

-- 
Cheers,

David / dhildenb