[PATCH v2 4/7] mm/vmalloc: Extend page table walk to support larger page_shift sizes and eliminate page table rewalk

[Mike Rapoport]

On Thu, 14 May 2026 17:41:05 +0800, Wen Jiang <jiangwenxiaomi at gmail.com> wrote:

Hi,

> 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().

After this patch we have two very simalar page table walkers:
vmap_pages_range_noflush_walk() and vmap_range_noflush().

The subtly differ at what levels they try huge mappings, how they
account page table modifucations and, at last vmap_range_noflush() is
left without support for contiguous mappings.

Is there a fundamental reason to have two page walkers?
Is there a reason not to support contiguous mappings in
vmap_range_noflush()?

-- 
Sincerely yours,
Mike.