Re: [PATCH v6 4/6] mm/vmalloc: Extend page table walk to support larger page_shift sizes and eliminate page table rewalk

[Wen Jiang]

On Mon, 13 Jul 2026 at 21:49, Dev Jain <dev.jain@xxxxxxx> wrote:
>
>
>
> On 09/07/26 1:08 pm, Wen Jiang wrote:
> > From: "Barry Song (Xiaomi)" <baohua@xxxxxxxxxx>
> >
> > vmap_pages_range_noflush_walk() (formerly 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 rewalk 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. Rename it to vmap_pages_range_noflush_walk()
> > since it now handles more than just small pages.
> >
> > For vmalloc() allocations with VM_ALLOW_HUGE_VMAP, we no longer need to
> > iterate over pages one by one via vmap_range_noflush(), which would
> > otherwise lead to page table rewalk. The code is now unified with the
> > PAGE_SHIFT case by simply calling vmap_pages_range_noflush_walk().
> >
> > Signed-off-by: Barry Song (Xiaomi) <baohua@xxxxxxxxxx>
> > Signed-off-by: Wen Jiang <jiangwen6@xxxxxxxxxx>
> > Tested-by: Xueyuan Chen <xueyuan.chen21@xxxxxxxxx>
> > Tested-by: Leo Yan <leo.yan@xxxxxxx>
> > Reviewed-by: Dev Jain <dev.jain@xxxxxxx>
> > ---
> >  mm/vmalloc.c | 81 ++++++++++++++++++++++++++++++----------------------
> >  1 file changed, 47 insertions(+), 34 deletions(-)
> >
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index d7fef85b241c4..d2a4d649af549 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -125,7 +125,8 @@ static int vmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
> >       pte_t *pte;
> >       u64 pfn;
> >       struct page *page;
> > -     unsigned long size = PAGE_SIZE;
> > +     unsigned long size;
> > +     unsigned int steps;
> >
> >       if (WARN_ON_ONCE(!PAGE_ALIGNED(end - addr)))
> >               return -EINVAL;
> > @@ -147,8 +148,8 @@ static int vmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
> >               }
> >
> >               size = vmap_set_ptes(pte, addr, end, pfn, prot, max_page_shift);
> > -             pfn += PFN_DOWN(size);
> > -     } while (pte += PFN_DOWN(size), addr += size, addr != end);
> > +             steps = PFN_DOWN(size);
> > +     } while (pte += steps, pfn += steps, addr += size, addr != end);
>
> I think I had also recommended to put these vmap_pte_range() changes
> into the previous patch.
>

Hi Dev

I put this change in patch 4 following Uladzislau's earlier suggestion:

https://lore.kernel.org/linux-mm/ah3Cn3YnefIVJDo2@milan/

Uladzislau, do you have a preference on where this hunk should go?

Thanks,
Wen