Re: [RFC PATCH 3/8] mm/vmalloc: Extend vmap_small_pages_range_noflush() to support larger page_shift sizes

[Barry Song <baohua@kernel.org>]

On Tue, Apr 14, 2026 at 12:08 AM Mike Rapoport <rppt@kernel.org> wrote:
>
> Hi Barry,

Thanks for reviewing, Mike!

>
> On Wed, Apr 08, 2026 at 10:51:10AM +0800, Barry Song (Xiaomi) wrote:
> > vmap_small_pages_range_noflush() provides a clean interface by taking
> > struct page **pages and mapping them via direct PTE iteration. This
> > avoids the page table zigzag seen when using
> > vmap_range_noflush() for page_shift values other than PAGE_SHIFT.
> >
> > Extend it to support larger page_shift values, and add PMD- and
> > contiguous-PTE mappings as well.
> >
> > Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
> > ---
> >  mm/vmalloc.c | 54 ++++++++++++++++++++++++++++++++++++++++------------
> >  1 file changed, 42 insertions(+), 12 deletions(-)
> >
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 57eae99d9909..5bf072297536 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -524,8 +524,9 @@ void vunmap_range(unsigned long addr, unsigned long end)
> >
> >  static int vmap_pages_pte_range(pmd_t *pmd, unsigned long addr,
> >               unsigned long end, pgprot_t prot, struct page **pages, int *nr,
> > -             pgtbl_mod_mask *mask)
> > +             pgtbl_mod_mask *mask, unsigned int shift)
> >  {
> > +     unsigned int steps = 1;
> >       int err = 0;
> >       pte_t *pte;
> >
> > @@ -543,6 +544,7 @@ static int vmap_pages_pte_range(pmd_t *pmd, unsigned long addr,
> >       do {
> >               struct page *page = pages[*nr];
> >
> > +             steps = 1;
> >               if (WARN_ON(!pte_none(ptep_get(pte)))) {
> >                       err = -EBUSY;
> >                       break;
> > @@ -556,9 +558,24 @@ static int vmap_pages_pte_range(pmd_t *pmd, unsigned long addr,
> >                       break;
> >               }
> >
> > +#ifdef CONFIG_HUGETLB_PAGE
>
> Why is this related to HUGETLB_PAGE?

This is also a question I asked myself during development.
Currently, huge mappings in mm/vmalloc have an ugly
dependency on HUGETLB, as hugetlb provides the APIs for
mapping multiple PTEs. Right now, set_ptes() is mainly used
for large folios in userspace; if it can fully support kernel
page tables, I would be very happy to remove this dependency
on HUGETLB entirely, including in the ioremap case in
vmap_pte_range().

I recall Ryan once mentioned some issues with using set_ptes()
for kernel mappings?

Once that issue is resolved, we can entirely remove the
HUGETLB dependency in mm/vmalloc.c.

>
> > +             if (shift != PAGE_SHIFT) {
> > +                     unsigned long pfn = page_to_pfn(page), size;
> > +
> > +                     size = arch_vmap_pte_range_map_size(addr, end, pfn, shift);
> > +                     if (size != PAGE_SIZE) {
> > +                             steps = size >> PAGE_SHIFT;
> > +                             pte_t entry = pfn_pte(pfn, prot);
> > +
> > +                             entry = arch_make_huge_pte(entry, ilog2(size), 0);
> > +                             set_huge_pte_at(&init_mm, addr, pte, entry, size);
> > +                             continue;
> > +                     }
> > +             }
> > +#endif
> > +
> >               set_pte_at(&init_mm, addr, pte, mk_pte(page, prot));
> > -             (*nr)++;
> > -     } while (pte++, addr += PAGE_SIZE, addr != end);
> > +     } while (pte += steps, *nr += steps, addr += PAGE_SIZE * steps, addr != end);
> >
> >       lazy_mmu_mode_disable();
> >       *mask |= PGTBL_PTE_MODIFIED;
> > @@ -568,7 +585,7 @@ static int vmap_pages_pte_range(pmd_t *pmd, unsigned long addr,
> >
> >  static int vmap_pages_pmd_range(pud_t *pud, unsigned long addr,
> >               unsigned long end, pgprot_t prot, struct page **pages, int *nr,
> > -             pgtbl_mod_mask *mask)
> > +             pgtbl_mod_mask *mask, unsigned int shift)
> >  {
> >       pmd_t *pmd;
> >       unsigned long next;
> > @@ -578,7 +595,20 @@ static int vmap_pages_pmd_range(pud_t *pud, unsigned long addr,
> >               return -ENOMEM;
> >       do {
> >               next = pmd_addr_end(addr, end);
> > -             if (vmap_pages_pte_range(pmd, addr, next, prot, pages, nr, mask))
> > +
> > +             if (shift == PMD_SHIFT) {
> > +                     struct page *page = pages[*nr];
> > +                     phys_addr_t phys_addr = page_to_phys(page);
> > +
> > +                     if (vmap_try_huge_pmd(pmd, addr, next, phys_addr, prot,
> > +                                             shift)) {
> > +                             *mask |= PGTBL_PMD_MODIFIED;
> > +                             *nr += 1 << (shift - PAGE_SHIFT);
> > +                             continue;
> > +                     }
>
> With this vmap_pages_pmd_range() looks quite similar to vmap_pmd_range().
> Any changes we can consolidate the two?

vmap_pmd_range() is for the ioremap case where we may have
8MB of contiguous memory. This is the case where we have
8MB total, but it is composed of 2MB chunks plus some
remainder. We might be able to extract some common code
though.

Thanks
Barry