Subject: Re: [PATCH v2 6/7] mm/vmalloc: align vm_area so vmap() can batch mappings

From: Uladzislau Rezki <[email-masked]>
Date: Wed, 20 May 2026 09:32:22 +0200

On Thu, May 14, 2026 at 05:41:07PM +0800, Wen Jiang wrote:
> From: "Barry Song (Xiaomi)" <[email-masked]>
> 
> Try to align the vmap virtual address to PMD_SHIFT or a
> larger PTE mapping size hinted by the architecture, so
> contiguous pages can be batch-mapped when setting PMD or
> PTE entries.
> 
> Signed-off-by: Barry Song (Xiaomi) <[email-masked]>
> Signed-off-by: Wen Jiang <[email-masked]>
> Tested-by: Xueyuan Chen <[email-masked]>
> ---
>  mm/vmalloc.c | 31 ++++++++++++++++++++++++++++++-
>  1 file changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index c30a7673e..b3389c8f1 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3591,6 +3591,35 @@ static int __vmap_huge(unsigned long addr, unsigned long end,
>  	return err;
>  }
>  
> +static struct vm_struct *get_aligned_vm_area(unsigned long size, unsigned long flags)
> +{
> +	unsigned int shift = (size >= PMD_SIZE) ? PMD_SHIFT :
> +				arch_vmap_pte_supported_shift(size);
> +	struct vm_struct *vm_area = NULL;
> +
> +	/*
> +	 * Try to allocate an aligned vm_area so contiguous pages can be
> +	 * mapped in batches.
> +	 */
> +	while (1) {
> +		unsigned long align = 1UL << shift;
> +
> +		vm_area = __get_vm_area_node(size, align, PAGE_SHIFT, flags,
> +				VMALLOC_START, VMALLOC_END,
> +				NUMA_NO_NODE, GFP_KERNEL,
> +				__builtin_return_address(0));
> +		if (vm_area || shift <= PAGE_SHIFT)
> +			goto out;
> +		if (shift == PMD_SHIFT)
> +			shift = arch_vmap_pte_supported_shift(size);
> +		else if (shift > PAGE_SHIFT)
> +			shift = PAGE_SHIFT;
> +	}
> +
> +out:
> +	return vm_area;
> +}
> +
IMO, we should get rid of this while(1) loop. It looks like you need to
handle just few cases. 3?

shift min value is PAGE_SHIFT, could you please clarify when it can be less?

--
Uladzislau Rezki