Re: [PATCH 2/6] mm/vmalloc: set area's page_order after allocation succeeds

[Uladzislau Rezki <urezki@gmail.com>]

On Sun, Aug 16, 2026 at 01:59:25PM +0300, Mike Rapoport (Microsoft) wrote:
> __vmalloc_area_node() calls set_vm_area_page_order() to set area's
> page_order before actually allocating pages to populate the area.
> 
> If allocation of large pages in HUGE_VMAP case fails midway, this leaves
> the area with elevated page_order throughout the cleanup path.
> 
> There is no actual issue with this because the only place that currently
> relies on area->page_order on the cleanup path is the loop calculating
> the direct map alias range in vm_reset_perms() and it anyway skips
> unpopulated pages.
> 
> But having set_vm_area_page_order() in the middle of __vmalloc_area_node()
> makes things very obscure, hard to reason about and error prone against
> future changes of the cleanup path.
> 
> Move the call to set_vm_area_page_order() after __vmalloc_area_node()
> succeeded where page order is guaranteed.
> 
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
>  mm/vmalloc.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 22566e0b6e38..6822f0fe9583 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3901,8 +3901,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
>  		goto fail;
>  	}
>  
> -	set_vm_area_page_order(area, page_shift - PAGE_SHIFT);
> -	page_order = vm_area_page_order(area);
> +	page_order = page_shift - PAGE_SHIFT;
>  
>  	/*
>  	 * High-order nofail allocations are really expensive and
> @@ -4106,6 +4105,14 @@ void *__vmalloc_node_range_noprof(unsigned long size, unsigned long align,
>  	if (!ret)
>  		goto fail;
>  
> +	/*
> +	 * Set area->page_order once it's known exactly that the order of the
> +	 * pages the area contains.
> +	 * Even if we succeeded to partially populate the area with large pages,
> +	 * still treat the area as populated with order-0 pages.
> +	 */
> +	set_vm_area_page_order(area, shift - PAGE_SHIFT);
> +
>  	/*
>  	 * Mark the pages as accessible, now that they are mapped.
>  	 * The condition for setting KASAN_VMALLOC_INIT should complement the
> 
> -- 
> 2.53.0
> 
OK, can we just set it right after the:

	area->nr_pages = vm_area_alloc_pages(
			vmalloc_gfp_adjust(gfp_mask, page_order), node,
			page_order, nr_small_pages, area->pages);


succeeds?

I am not sure there is a good reason to move it out of the
__vmalloc_area_node().

--
Uladzislau Rezki

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