Re: [PATCHv6 06/17] LoongArch/mm: Align vmemmap to maximal folio size

Kiryl Shutsemau
2026-02-05T13:52:38Z

On Wed, Feb 04, 2026 at 05:56:45PM +0100, David Hildenbrand (arm) wrote:
> On 2/2/26 16:56, Kiryl Shutsemau wrote:
> > The upcoming change to the HugeTLB vmemmap optimization (HVO) requires
> > struct pages of the head page to be naturally aligned with regard to the
> > folio size.
> >
> > Align vmemmap to MAX_FOLIO_NR_PAGES.
> >
> > Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
> > ---
> > arch/loongarch/include/asm/pgtable.h | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
> > index c33b3bcb733e..f9416acb9156 100644
> > --- a/arch/loongarch/include/asm/pgtable.h
> > +++ b/arch/loongarch/include/asm/pgtable.h
> > @@ -113,7 +113,8 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
> > min(PTRS_PER_PGD * PTRS_PER_PUD * PTRS_PER_PMD * PTRS_PER_PTE * PAGE_SIZE, (1UL << cpu_vabits) / 2) - PMD_SIZE - VMEMMAP_SIZE - KFENCE_AREA_SIZE)
> > #endif
> > -#define vmemmap ((struct page *)((VMALLOC_END + PMD_SIZE) & PMD_MASK))
> > +#define VMEMMAP_ALIGN max(PMD_SIZE, MAX_FOLIO_NR_PAGES * sizeof(struct page))
> > +#define vmemmap ((struct page *)(ALIGN(VMALLOC_END, VMEMMAP_ALIGN)))
>
>
> Same comment, the "MAX_FOLIO_NR_PAGES * sizeof(struct page)" is just black magic here
> and the description of the situation is wrong.
>
> Maybe you want to pull the magic "MAX_FOLIO_NR_PAGES * sizeof(struct page)" into the core and call it
>
> #define MAX_FOLIO_VMEMMAP_ALIGN (MAX_FOLIO_NR_PAGES * sizeof(struct page))
>
> But then special case it base on (a) HVO being configured in an (b) HVO being possible
>
> #ifdef HUGETLB_PAGE_OPTIMIZE_VMEMMAP && is_power_of_2(sizeof(struct page)

This would require some kind of asm-offsets.c/bounds.c magic to pull the
struct page size condition to the preprocessor level.

--
Kiryl Shutsemau / Kirill A. Shutemov