Subject: Re: [PATCH v3 6/6] mm/vmalloc: align vm_area so vmap() can batch mappings

From: Dev Jain <[email-masked]>
Date: Wed, 27 May 2026 11:55:17 +0530

On 22/05/26 11:01 am, 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]>

Hmm okay I would have preferred to squash this in the previous, but
the correctness of previous patch does not rely on this, so it's fine.

> ---
>  mm/vmalloc.c | 33 ++++++++++++++++++++++++++++++++-
>  1 file changed, 32 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 50642246f4d40..040d400928aab 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3620,6 +3620,37 @@ static int vmap_batched(unsigned long addr, unsigned long end,
>  	return err;
>  }
>  

This is screaming for a helper :)

> +static struct vm_struct *get_aligned_vm_area(unsigned long size,
> +		unsigned long flags, const void *caller)

Call this vmap_get_aligned_vm_area, then ...

> +{
> +	struct vm_struct *vm_area;
> +	unsigned int shift;
> +
> +	/* Try PMD alignment for large sizes */
> +	if (size >= PMD_SIZE) {
> +		vm_area = __get_vm_area_node(size, PMD_SIZE, PAGE_SHIFT, flags,
> +				VMALLOC_START, VMALLOC_END,
> +				NUMA_NO_NODE, GFP_KERNEL, caller);

Add a wrapper over this called __get_vm_area_node_aligned_caller, which can
call __get_vm_area_node() with all other arguments fixed, except "align".

> +		if (vm_area)
> +			return vm_area;
> +	}
> +
> +	/* Try CONT_PTE alignment */
> +	shift = arch_vmap_pte_supported_shift(size);
> +	if (shift > PAGE_SHIFT) {
> +		vm_area = __get_vm_area_node(size, 1UL << shift, PAGE_SHIFT, flags,
> +				VMALLOC_START, VMALLOC_END,
> +				NUMA_NO_NODE, GFP_KERNEL, caller);
> +		if (vm_area)
> +			return vm_area;
> +	}
> +
> +	/* Fall back to page alignment */
> +	return __get_vm_area_node(size, PAGE_SIZE, PAGE_SHIFT, flags,
> +			VMALLOC_START, VMALLOC_END,
> +			NUMA_NO_NODE, GFP_KERNEL, caller);
> +}
> +
>  /**
>   * vmap - map an array of pages into virtually contiguous space
>   * @pages: array of page pointers
> @@ -3658,7 +3689,7 @@ void *vmap(struct page **pages, unsigned int count,
>  		return NULL;
>  
>  	size = (unsigned long)count << PAGE_SHIFT;
> -	area = get_vm_area_caller(size, flags, __builtin_return_address(0));
> +	area = get_aligned_vm_area(size, flags, __builtin_return_address(0));
>  	if (!area)
>  		return NULL;
>