Re: [PATCH v6 4/9] mm: thp: Introduce anon_orders and anon_always_mask sysfs files

[David Hildenbrand]

On 10.10.23 02:20, Andrew Morton wrote:
> On Sun, 08 Oct 2023 09:54:22 +1100 Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote:
>
> > > 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