Re: [PATCH v3] mm/hugetlb: fix hugetlb vs. core-mm PT locking

[David Hildenbrand]

> > pte_alloc_one() ends up calling pte_fragment_alloc(mm, 0). But there we always
> > end up calling pagetable_alloc(, 0).
> >
> > And fragments are supposed to be <= a single page.
> >
> > Now I'm confused what's wrong here ... am I missing something obvious?
> >
> > CCing some powerpc folks. Is this some pte_t oddity?
>
> It will be because PTRS_PER_PTE is not a compile time constant :(

Oh, sneaky! Thanks a bunch!

>    $ git grep "define PTRS_PER_PTE" arch/powerpc/include/asm/book3s/64
>    arch/powerpc/include/asm/book3s/64/pgtable.h:#define PTRS_PER_PTE        (1 << PTE_INDEX_SIZE)
>    
>    $ git grep "define PTE_INDEX_SIZE" arch/powerpc/include/asm/book3s/64
>    arch/powerpc/include/asm/book3s/64/pgtable.h:#define PTE_INDEX_SIZE  __pte_index_size
>    
>    $ git grep __pte_index_size arch/powerpc/mm/pgtable_64.c
>    arch/powerpc/mm/pgtable_64.c:unsigned long __pte_index_size;
>
> Which is because the pseries/powernv (book3s64) kernel supports either
> the HPT or Radix MMU at runtime, and they have different page table
> geometry.
>
> If you change it to use MAX_PTRS_PER_PTE it should work (that's defined
> for all arches).

Yes, that should fly, thanks again!

--
Cheers,

David / dhildenb