[RFC PATCH 4/8] mm/vmalloc: Eliminate page table zigzag for huge vmalloc mappings

Barry Song (Xiaomi)
2026-04-08T02:51:49Z

For vmalloc() allocations with VM_ALLOW_HUGE_VMAP, we no longer
need to iterate over pages one by one, which would otherwise lead to
zigzag page table mappings.

The code is now unified with the PAGE_SHIFT case by simply
calling vmap_small_pages_range_noflush().

Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
mm/vmalloc.c | 22 ++++------------------
1 file changed, 4 insertions(+), 18 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 5bf072297536..eba436386929 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -689,27 +689,13 @@ static int vmap_small_pages_range_noflush(unsigned long addr, unsigned long end,
int __vmap_pages_range_noflush(unsigned long addr, unsigned long end,
pgprot_t prot, struct page **pages, unsigned int page_shift)
{
- unsigned int i, nr = (end - addr) >> PAGE_SHIFT;
-
WARN_ON(page_shift < PAGE_SHIFT);

- if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC) ||
- page_shift == PAGE_SHIFT)
- return vmap_small_pages_range_noflush(addr, end, prot, pages, PAGE_SHIFT);
-
- for (i = 0; i < nr; i += 1U << (page_shift - PAGE_SHIFT)) {
- int err;
-
- err = vmap_range_noflush(addr, addr + (1UL << page_shift),
- page_to_phys(pages[i]), prot,
- page_shift);
- if (err)
- return err;
+ if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC))
+ page_shift = PAGE_SHIFT;

- addr += 1UL << page_shift;
- }
-
- return 0;
+ return vmap_small_pages_range_noflush(addr, end, prot, pages,
+ min(page_shift, PMD_SHIFT));
}

int vmap_pages_range_noflush(unsigned long addr, unsigned long end,
--
2.39.3 (Apple Git-146)