On Wed, Sep 23, 2026 at 02:28:31PM +0800, Wen Jiang wrote:
> From: "Barry Song (Xiaomi)" <[email protected]>
>
> In many cases, the pages passed to vmap() may include high-order
> pages. For example, the systemheap often allocates pages in descending
> order: order 8, then 4, then 0. Currently, vmap() iterates over every
> page individually—even pages inside a high-order block are handled
> one by one.
>
> This patch detects physically contiguous pages (regardless of whether
> they are compound or non-compound) by scanning with
> num_pages_contiguous(), and maps them as a single contiguous block
> whenever possible. The mapping order is determined by taking the
> minimum of the contiguous page count and the pfn alignment, allowing
> graceful degradation when pfn alignment is less than the contiguous
> range.
>
> Pages with the same page_shift are coalesced and mapped via
> vmap_pages_range_noflush_walk() to avoid page table rewalk.
>
> As users typically allocate memory in descending orders (e.g.
> 8 → 4 → 0), once an order-0 page is encountered, we stop scanning
> for contiguous pages since subsequent pages are likely order-0 as well.
>
> Signed-off-by: Barry Song (Xiaomi) <[email protected]>
> Co-developed-by: Dev Jain <[email protected]>
> Signed-off-by: Dev Jain <[email protected]>
> Signed-off-by: Wen Jiang <[email protected]>
> Tested-by: Xueyuan Chen <[email protected]>
> Tested-by: Leo Yan <[email protected]>
> ---
> mm/vmalloc.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 80 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index a43965016eb4d..37cddb7f45a4f 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3576,6 +3576,85 @@ static inline unsigned int vm_shift(pgprot_t prot,
> unsigned long size)
> return arch_vmap_pte_supported_shift(size);
> }
>
> +static inline int get_vmap_batch_order(struct page **pages,
> + pgprot_t prot, unsigned int nr_pages)
>
get_vmap_mapping_order()?
> +{
> + unsigned long pfn;
> + unsigned int nr_contig;
> + int order;
> +
> + if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMAP))
> + return 0;
> +
> + /* Limit nr_pages by pfn alignment */
> + pfn = page_to_pfn(*pages);
> + if (pfn > 0)
> + nr_pages = min_t(size_t, nr_pages, 1UL << __ffs(pfn));
> +
> + nr_contig = num_pages_contiguous(pages, nr_pages);
> + if (nr_contig < 2)
> + return 0;
> +
> + order = ilog2(nr_contig);
> +
> + if (vm_shift(prot, PAGE_SIZE << order) == PAGE_SHIFT)
> + return 0;
> +
> + return order;
> +}
> +
> +static int vmap_pages_range_batched(unsigned long addr, unsigned long end,
> + pgprot_t prot, struct page **pages)
> +{
> + const unsigned int nr_pages = (end - addr) >> PAGE_SHIFT;
> + unsigned int prev_shift = 0, batch_idx = 0;
> + unsigned long batch_start = addr, batch_end = addr;
> + int err;
> +
> + err = kmsan_vmap_pages_range_noflush(addr, end, prot, pages,
> + PAGE_SHIFT, GFP_KERNEL);
> +
> + if (err)
> + goto out;
> +
> + for (unsigned int i = 0; i < nr_pages; ) {
> + unsigned int shift = PAGE_SHIFT +
> + get_vmap_batch_order(pages + i, prot, nr_pages - i);
> +
> + if (!i)
> + prev_shift = shift;
> +
> + if (shift != prev_shift) {
> + err = vmap_pages_range_noflush_walk(batch_start,
> batch_end,
> + prot, pages + batch_idx, prev_shift);
> + if (err)
> + goto out;
> + prev_shift = shift;
> + batch_start = batch_end;
> + batch_idx = i;
> + }
> +
> + /*
> + * Once we fail to batch pages, we expect to fail batching
> + * for all remaining pages, so just give up.
> + */
> + if (shift == PAGE_SHIFT)
> + break;
> +
> + batch_end += 1UL << shift;
> + i += 1U << (shift - PAGE_SHIFT);
> + }
> +
> + /* Remaining */
> + if (batch_start < end)
> + err = vmap_pages_range_noflush_walk(batch_start, end, prot,
> + pages + batch_idx, prev_shift);
> +
> +out:
> + flush_cache_vmap(addr, end);
> + return err;
>
On error, if kmsan_vmap_pages_range_noflush() succeed you do not do a
proper cleanup?
i.e. to cleanup KMSAN metadata: kmsan_vunmap_range_noflush(addr, end);
> +}
> +
> /**
> * vmap - map an array of pages into virtually contiguous space
> * @pages: array of page pointers
> @@ -3619,8 +3698,7 @@ void *vmap(struct page **pages, unsigned int count,
> return NULL;
>
> addr = (unsigned long)area->addr;
> - if (vmap_pages_range(addr, addr + size, pgprot_nx(prot),
> - pages, PAGE_SHIFT) < 0) {
> + if (vmap_pages_range_batched(addr, addr + size, pgprot_nx(prot), pages)
> < 0) {
> vunmap(area->addr);
> return NULL;
> }
> --
> 2.34.1
>
