Re: [PATCH v8 1/6] mm/vmalloc: extract vm_area_free_pages() helper from vfree()

[Uladzislau Rezki <urezki@gmail.com>]

On Fri, Mar 27, 2026 at 03:18:37PM +0530, Shivam Kalra via B4 Relay wrote:
> From: Shivam Kalra <shivamkalra98@zohomail.in>
> 
> Extract the page-freeing loop and NR_VMALLOC stat accounting from
> vfree() into a reusable vm_area_free_pages() helper. The helper operates
> on a range [start_idx, end_idx) of pages from a vm_struct, making it
> suitable for both full free (vfree) and partial free (upcoming vrealloc
> shrink).
> 
> Freed page pointers in vm->pages[] are set to NULL to prevent stale
> references when the vm_struct outlives the free (as in vrealloc shrink).
> 
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> Signed-off-by: Shivam Kalra <shivamkalra98@zohomail.in>
> ---
>  mm/vmalloc.c | 47 +++++++++++++++++++++++++++++++++--------------
>  1 file changed, 33 insertions(+), 14 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index d75151649c97..79a57955345d 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3416,6 +3416,38 @@ void vfree_atomic(const void *addr)
>  		schedule_work(&p->wq);
>  }
>  
> +/*
> + * vm_area_free_pages - free a range of pages from a vmalloc allocation
> + * @vm: the vm_struct containing the pages
> + * @start_idx: first page index to free (inclusive)
> + * @end_idx: last page index to free (exclusive)
> + *
> + * Free pages [start_idx, end_idx) updating NR_VMALLOC stat accounting.
> + * Freed vm->pages[] entries are set to NULL.
> + * Caller is responsible for unmapping (vunmap_range) and KASAN
> + * poisoning before calling this.
> + */
> +static void vm_area_free_pages(struct vm_struct *vm, unsigned int start_idx,
> +			       unsigned int end_idx)
> +{
> +	unsigned int i;
> +
> +	for (i = start_idx; i < end_idx; i++) {
> +		struct page *page = vm->pages[i];
> +
> +		BUG_ON(!page);
> +		/*
> +		 * High-order allocs for huge vmallocs are split, so
> +		 * can be freed as an array of order-0 allocations
> +		 */
> +		if (!(vm->flags & VM_MAP_PUT_PAGES))
> +			mod_lruvec_page_state(page, NR_VMALLOC, -1);
> +		__free_page(page);
> +		vm->pages[i] = NULL;
> +		cond_resched();
> +	}
> +}
> +
>  /**
>   * vfree - Release memory allocated by vmalloc()
>   * @addr:  Memory base address
> @@ -3436,7 +3468,6 @@ void vfree_atomic(const void *addr)
>  void vfree(const void *addr)
>  {
>  	struct vm_struct *vm;
> -	int i;
>  
>  	if (unlikely(in_interrupt())) {
>  		vfree_atomic(addr);
> @@ -3459,19 +3490,7 @@ void vfree(const void *addr)
>  
>  	if (unlikely(vm->flags & VM_FLUSH_RESET_PERMS))
>  		vm_reset_perms(vm);
> -	for (i = 0; i < vm->nr_pages; i++) {
> -		struct page *page = vm->pages[i];
> -
> -		BUG_ON(!page);
> -		/*
> -		 * High-order allocs for huge vmallocs are split, so
> -		 * can be freed as an array of order-0 allocations
> -		 */
> -		if (!(vm->flags & VM_MAP_PUT_PAGES))
> -			mod_lruvec_page_state(page, NR_VMALLOC, -1);
> -		__free_page(page);
> -		cond_resched();
> -	}
> +	vm_area_free_pages(vm, 0, vm->nr_pages);
>  	kvfree(vm->pages);
>  	kfree(vm);
>  }
> 
> -- 
> 2.43.0
> 
> 
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

--
Uladzislau Rezki